The mind-body problem in the philosophy of mind and cognitive neuroscience: a physicalist naturalist solution
Using an analysis of a voluntary action caused by a visual perception, I suggest that the three fundamental characteristics of this perception (being conscious, self-conscious, and provided with a content) are neurologically implemented by three distinct higher order properties of brain dynamics. This hypothesis allows me to sketch out a physicalist naturalist solution to the mind-body problem. According to this solution, primary phenomenal consciousness is neither a non-physical substance, nor a non-physical property but simply the “format” that the brain gives to a part of its dynamics in order to obtain a fine tuning with its environment when the body acts on it.
KeywordsCognitive neuroscience Epistemology Consciousness Self Intentionality Mind-body problem
The mind-body problem
I am driving, I see that the traffic light is red, then I brake and stop my car. My conscious perception that the traffic light appears to me to be red is caused by the fact that according to common sense the traffic light is actually red. This perception in turn causes together with other conscious or unconscious mental states and dispositions of mine my action of pressing the brake pedal. In the language of folk psychology, this reconstruction of my action is also a good explanation of why I stopped my car: The traffic light was red!
However, if you shift from the language of folk psychology to the language of physics and other natural sciences, you can see that when you say that a traffic light is red, you mean that a lamp inside the traffic light emits electromagnetic waves with a length comprised between 620 and 750 nm. These electromagnetic waves are the true distal stimulus of my perception: A colorless physical event that is very different from the content of my perception. In the language of the hard sciences, this stimulus is the cause of the brain processes that in turn cause the motor response of pressing the brakes.
What is the relationship between the two descriptions (and implicitly explanations) of my voluntary action, the former formulated in the language of folk psychology and the latter in the language of physics, chemistry, and biology? In the final analysis, this is the essence of the mind-body problem! The solutions given to this problem are numerous , but the fundamental ones from classical antiquity up until today are three: “mind-body dualism” , “physicalism” , and “functionalism” or “cognitivism” .
According to interactionist ontological dualism, the causal chain that goes from the distal stimulus to the motor response is interrupted inside the brain by the intervention of the conscious mind qua entity or property extraneous to the physical world. According to Cartesian dualists, without this interference of my conscious mind in the activity of my brain, my action would not be voluntary. But what neurological studies attest to the existence of such interference by the conscious mind in brain activity during the sensorimotor coordination process that takes place when a voluntary action is performed? Many studies seem to attest to the opposite! According to B. Libet and many other neuroscientists, the awareness of moving a finger only arises in the mind after the occurrence of readiness potentials in the brain that are either the real cause of the movement or at least occur simultaneously with the real cause . Whatever the judgment on Libet’s and other similar experiments, interactionist ontological dualism is in any case incompatible with a scientific conception of the world because it requires in the case of voluntary actions the existence of a “spiritual” non-physical substance or property capable of interfering in the brain with the causal chains of physical events that connect sensory stimuli to motor responses. Such a dualism violates the principle of the causal closure of the physical world  and, consequently, violates the principle of energy conservation as well.
ᅟAccording to physicalism, the causal chain that goes from a distal stimulus to the motor response that it triggers is uninterrupted. There is no interference of the mind on the brain. Physicalists think that the mind does not exist according to its ontological-dualist meaning. However, they do not believe that mind and consciousness do not exist! They do recognize that mental states in general and states of consciousness in particular contribute to causally determining our observable behavior. But according to them, the mind can play a causal role, influencing the brain only because it is itself a part of brain activity!
However, physicalists have to face an objection that has condemned them to be almost always in the minority among philosophers and scientists from antiquity to today: The phenomenological gap existing between mental states and their neuronal correlates seems to imply that reducing mental states to brain processes is impossible. For example, why do you see a blue spot if certain retinal cones of yours react to electromagnetic waves having a length between 400 and 450 nm? What does a certain wavelength have in common with a certain color? And, more generally, what do the physical properties of any neuronal correlate have in common with the qualities (colors, flavors, sounds, etc., but also pain, pleasure, and other emotions) that are the content of your conscious and subjective experience? Is it possible that things looking so different are actually the same? Those who were able to answer this question would solve the problem that was called by D. Chalmers the “hard problem” par excellence . Critics of physicalism are convinced that the “hard problem” cannot be solved, and therefore, they think that physicalism is false.
To avoid the difficulties posed by the “hard problem,” many philosophers, psychologists, and neuroscientists have sought and still seek solutions to the mind-body problem that allow them to get rid of physicalism without falling back into ontological dualism. Among these “third ways” between ontological dualism and physicalism, the most important one is functionalism (or cognitivism).
According to functionalists, in order to identify a mental state, it is sufficient to redescribe it by its causes and effects, that is, to consider it as an intermediate step between a sensory stimulus and the motor response triggered by it. The contribution of functionalism to the cognitive sciences must not be underestimated. No solution to the mind-body problem that is minimally believable can claim that psychology is integrally translatable into the language of neurosciences. However, complete separation between psychology and neurosciences is equally unacceptable. Simply redescribing a state of mind as a state capable of carrying out a specific function in the brain is not sufficient to explain how this capacity is concretely realized. A preliminary idea of at least one of its possible implementations is necessary. Therefore, no coherent general scientific worldview can avoid offering at least the trace of a plausible solution to the “hard problem.”
“Emergentist dualism”—Consciousness emerges from brain activity, but after its emergence, it constitutes a level of reality independent of the physical world and can causally retroact on it. Therefore, consciousness violates the principle of closure of the physical world when it retroacts on the brain. Consequently, emergentist dualism has to confront all the objections that can be made to interactionist ontological dualism.
“Emergentist functionalism”—Consciousness “emerges” from brain activity only in the weak sense that it is a virtual reality (that is, software) somehow implemented by the activity of that particular hardware (or “wetware”) that is the brain. But no one exactly knows how this implementation is possible. This weak version of emergentism actually coincides with functionalism and meets the same objection: It excessively separates cognitive psychology from cognitive neuroscience.
“Emergentist physicalism”—The mind, including consciousness, is a set of higher order properties of those brain dynamics that emerge from the activity of individual neurons exactly as the heat of a gas emerges from the motion of its individual molecules qua average kinetic energy. According to this interpretation of emergentism, the mind qua a set of higher order properties of brain dynamics is certainly ontologically distinguishable from the local activity of single neuronal groups but its retroaction on the local activity of single neuronal groups does not violate the principle of closure of the physical world because the very mind is something physical qua a set of higher order properties of brain dynamics! Therefore, this form of emergentism is perfectly compatible with physicalism and indeed contains an idea of great interest that I will try to clarify and develop later: mental states are ontologically reducible not directly to the activity of single neuronal groups but to certain higher order (that is, systemic) properties of general brain dynamics. However, in adopting this position, one must be very careful not to fall into the trick on which the deceptive success of today’s emergentism is based: confusing the dualist version of this theory with its physicalist version, and believing that thanks to this conceptual confusion, one can reconcile dualism with a scientific worldview.
With respect to the mind-body problem, neuroscientists and philosophers are currently divided into two large groups. The philosophers and neuroscientists of the first group opt for “naturalism” , especially for a kind of naturalism oriented towards physicalism or functionalism. According to naturalism, a solution to the mind-body problem can be found only thanks to collaboration between the study of the mind (psychology and philosophy) and the study of the brain (neurosciences). By contrast, the philosophers and neuroscientists of the second group criticize any form of naturalism and think that the study of the mind cannot be conducted in accordance with the methods of natural science. Some of them actually defend a return to dualism.
Among the naturalists, neuroscientists predominate  but some well-known philosophers of the mind are also naturalists . Among the anti-naturalists, philosophers are instead more numerous (some of them are openly dualist  while others are only anti-physicalist ) but some psychologists and neuroscientists are also against the reduction of the mind to brain activity .
Here, I would like to defend from a philosophical point of view the arguments for a kind of strong naturalism (or better emergentist physicalism), that is, I would like to show by the conceptual analysis of my previous example of a voluntary action—stopping my car in front of a traffic light that is red—that the reduction of mental states to higher order properties of brain dynamics is the most reasonable solution to the mind-body problem and that, to reach this conclusion, a philosopher can make use of many theories and many empirical data offered by cognitive neuroscience. It is up to neuroscientists to judge whether this naturalistic philosophical solution of the mind-body problem is of any use to them!
Intentionality, self-consciousness, and consciousness
The first difficulty faced by a physicalist naturalist is to find out what the neuronal correlates of the states of consciousness could be. For example, every perception (like the visual perception of my example) is a lived experience in which three different characteristics are fused together: (1) to have Intentionality, here with a capital letter to indicate the peculiar philosophical sense to have a content, (2) to be a state of phenomenal self-consciousness, and (3) to be a state of phenomenal consciousness (more precisely to be, like all perceptions, a state of the “primary consciousness”  that human beings have in common with many other animals). I see that the traffic light is red and not green (Intentionality), I know it is me who sees that the traffic light is red, that is, I refer my perception to myself (self-consciousness or “Ego”), and being awake and attentive, I am directly aware of both these characteristics of my perception (phenomenal consciousness). So, are these three characteristics fused in my brain as they are fused in my lived experience or are they instead implemented by distinct and in principle separable brain processes?
The second hypothesis is the most likely one since in patients affected by several neurological diseases or mutilations, these three characteristics appear separately. For example, very well-known cases of blindsight tell us that patients who have undergone a surgical separation of their brain hemispheres are able to correctly guess whether the bar that appears in their left visual field is horizontal or vertical in more than 50% of cases although they sincerely declare that they see no bar. This is a proof of the existence in their right hemisphere of a “visual” perception not accompanied by consciousness, that is, an activity of the brain that, although unconscious, carries information about the position of the bar and therefore can be considered a “visual perception” from the functional point of view . By contrast, blind patients affected by the Anton-Babinski syndrome have the impression of not being blind, that is, they are aware of having perceptions that in fact, they do not have from a functional point of view . Therefore, if these clinical cases are reliable, as they seem to be, Intentionality and phenomenal consciousness are two distinct and sometimes separate phenomena.
Similarly, the “alien hand syndrome” shows that, due to a specific pathology, some patients may behave as if their hands were guided by two different “Egos” which have sometimes opposite intentions although this strange behavior appears in subjects who at that moment are fully conscious (awake and alert) in a completely normal way . In this case, it is self-consciousness that presents itself as a brain phenomenon at least in part distinct from phenomenal consciousness.
Therefore, if you want to search a naturalistic reduction of mental states that are simultaneously Intentional, conscious, and self-conscious, you must advance the hypothesis that these three characteristics are respectively identical to three distinct functional states of the brain implemented by brain processes that are equally distinct although not without any reciprocal interactions.
The naturalistic reduction of intentionality
If in my seeing that the traffic light is red, the conscious and self-conscious character of my perception is temporarily canceled, the residual is a purely Intentional state (“See(Red*)”), that is, a state of the brain that can be considered mental in a residual sense only because it has an internal content. And this content is the fact that the traffic light appears to be red (“Red*”). It is precisely thanks to this internal content that my perception refers to the external fact that the semaphore is actually red (“Red” according to the description given by common sense). Therefore, if you take into account that according to common sense the fact that the traffic light is actually red is the main cause (“➔”) of the fact that it appears to be red and this Intentional state on its turn is the cause (together with other mental states “M”) of the action “A” of stopping the car, you can give the following “philosophical reconstruction” of this Intentional state:
If the relation of the mind to the external world is called “Intentionality” and is represented here by the symbol “⇒,” then the Intentional relation of my perception to the fact that the traffic light is red can be represented as follows: “See(Red*) ⇒ Red”. Therefore, temporarily putting in brackets the conscious and subjective character of my perception allows me to isolate an internal state within this perception that has notable similarities, for example, with the internal states of the devices that drive the experimental prototypes of self-driving cars. These cars, although they are not conscious and self-conscious, nevertheless must be equipped with an electronic driving system (their “mind”) that enables them to stop when they are in front of a red traffic light. In other words, if you do not take into account the act of seeing something as a conscious and self-conscious act and consider only the functional “seeing” (“f-See”) that is common to a human being and to the driving system of a self-driving car, then you must admit that any physical state capable of transforming the information conveyed by the electromagnetic waves that are emitted by the red traffic light into a command to activate the brakes can be considered as a physically implemented “f-See.”
Therefore, following F.I. Dretske , I shall replace the mysterious relationship of Intentionality (“⇒”) that according to folk psychology seems to exist between the mind and the physical world with relations of cause and effect (“→”) between physical events: “I see that the traffic light is red” means in functional terms that electromagnetic waves of a certain kind (that is, the distal stimulus “DS-Red”) produce in my brain a physical implementation of the functional Intentional state of “f-seeing” that the traffic light is red. And this state (together with other functional states “f-M”) causes the action “A” of stopping the car:
However, “Red*” is a quale. Therefore, in order to obtain a “functional reduction” of the Intentional state “See(Red*)” without eliminating the causal role played by the content “Red*” in the production of the action “A,” you can resort to the adverbial theory of perception . Since “f-See” is a purely functional state and is neither conscious nor self-conscious, you can take its supposed content into account only in view of the function that it plays in the process that causally links the distal stimulus “DS-Red” to the motor response “R” (=“A”). In order to carry out that function, it is not necessary that “f-See” has a content in the proper sense, that is, a content I am conscious of. It is sufficient that “f-See” is a functional state of my brain that is caused by the presence of a red traffic light and in turn causes my action of braking. Therefore, by applying the adverbial theory of perception, I can substitute “Red*” with the adverb “redly” and replace “See(Red*)” with “redly(f-See)”. With this substitution, the content of my visual perception is replaced by a certain way of seeing. Therefore, with regard to my brain (as well as to the driving system of a self-driving car), the “functional reduction” of (1a) can be formulated as a causal chain of this kind:
However, the functional reduction of Intentionality is necessary but not sufficient to naturalize it. To reach such a naturalization, it is also necessary to clarify in advance how certain higher order (or systemic) properties of brain dynamics can emerge from the interaction of single neuronal groups. Important indications regarding this process can be found in the hypotheses advanced by G. Edelman and G. Tononi , and some philosophers as well . If you apply these hypotheses to the example of my seeing that the traffic light is red, you can argue that this perception, like the perception of any other qualia (visual, acoustic, tactile qualia, etc.), is implemented by a complex system of modulation processes of brain activity obtained by the appropriately distributed release of neuro-modulators produced by basal ganglia throughout the brain and, more generally, by the activity of the “dynamic core” . From this point of view, it must be assumed that the functional reduction of the perception that the traffic light is red (that is, “redly(f-See)”), is implemented by a certain kind of neuro-modulation of brain dynamics. I symbolically indicate this process of neuro-modulation by “nm3(d)”: “d” indicates the aspect of brain dynamics that implements visual perceptions in general, and “nm3” indicates the particular neuro-modulation of “d” that usually obtains, in a complex and distributed way, in certain parts of the human brain whenever it receives a signal produced by a distal stimulus of the same type as “DS-Red” from the eyes and consequently triggers the execution of a motor response of the same type as “R”.
To sum up, the brain dynamics that implement the functional reduction of the perception (qua Intentional state) that the traffic light is red can symbolically be represented as follows (“B” is the brain implementation of “f-M”):
Finally, again following Edelman and Tononi, the neuro-modulation “nm3” of “d” can be considered a higher order property emerging in the dynamic core from certain neuronal processes (I shall call them “np3”) and their combination with activity in the rest of the brain (“B”). Therefore, this is a “physico-neuronal implementation” of (3a):
Moreover, it should be noted that the same higher order property of brain dynamics (e.g., “nm3”) can be implemented by distinct neuronal processes (e.g., “np3” or “np4”) which Edelman calls “degenerate” . This allows us to defend physicalism from the objection raised by functionalists through the theory of “multiple realizability.” According to this objection, a mental state, being implementable by different neuronal processes, cannot be identical to any of them. If it were so, it would be simultaneously identical to different things and, therefore, would be different from itself. This objection can be avoided if you distinguish the higher order properties of brain dynamics from the different degenerate neuronal processes from which the higher order properties emerge (see “physicalist emergentism”): The functional state to which a mental state is functionally reducible is ontologically identical to a single higher order property of brain dynamics in agreement with physicalism whereas this higher order property can emerge from different degenerate neuronal processes in agreement with the functionalist theory of multiple realizability.
To sum up, the ontological reduction of the Intentionality of a mental state like a perception is a three-step procedure.
First step: functional reduction of the Intentionality of the mental state to a functional state of the brain.
Second step: clarification of how higher order properties of brain dynamics can implement the functional state mentioned above.
Third step: clarification of how each higher order property of brain dynamics can emerge from different possibly degenerate neuronal processes.
On the whole, the naturalistic reduction of the fact that I stop the car because I see that the traffic light is red can be so summarized:
1a) Red → ((See(Red∗)) and M) → A Philosophical Reconstruction.
2a) DS ‐ Red → (redly(f ‐ See) and f ‐ M) → R(=A) Functional Reduction of (1a).
3a) DS ‐ Red → (nm3(d) and B) → R Systemic Brain Implementation of (2a).
4a) DS ‐ Red → (np3 and B) → R The Neuronal Processes from which (3a) emerges.
The naturalistic reduction of consciousness and self-consciousness
I have functionally reduced the Intentionality of my visual perception by substituting in its philosophical reconstruction “See(Red*)” with “redly(f-See).” Similarly, I can functionally reduce the conscious and self-conscious character of that perception (“consciously(See(I, Red*))”) by substituting “redly(f-See)” in (2a) with “consciously(subjectively(redly(f-See))).” The adverb “consciously” represents “functional consciousness,” that is, the functional reduction of the fact that my perception is a state of “phenomenal consciousness” whereas the adverb “subjectively” represents “functional self-consciousness,” that is, it is the functional reduction of the fact that my perception is a state of “phenomenal self-consciousness” (or “Ego”). Thanks to this substitution and other similar modifications I obtain the “complete naturalistic reduction” of my perception and my subsequent voluntary action:
In (3b), “nm1,” “nm2,” and “nm3” symbolically represent the neuro-modulations that respectively transform the brain dynamics symbolized by “d” into the complete physical implementation of my conscious, subjective, and Intentional perception. In other words, the brain dynamics “d,” if successively neuro-modulated by “nm3,” “nm2,” and “nm1” in this order like in a Chinese box game, becomes the complete systemic brain implementation of my visual perception that the traffic light is red. First of all, “nm3” transforms “d” into the physical implementation “nm3(d)” of the functional reduction of an Intentional state. Secondly, “nm2” transforms “nm3(d)” into the physical implementation “nm2(nm3(d))” of a subjective Intentional state, that is, it connects a certain amount of information that circulates in my brain with the representation that my brain gives of its own activity and the activity of the rest of the body. This connection is necessary to achieve good sensorimotor coordination . Finally, “nm1” transforms “nm2(nm3(d))” into the physical implementation “nm1(nm2(nm3(d)))” of my conscious perception. This last transformation is necessary because the sensorimotor coordination offered by “nm2” and “nm3” would not be sufficient to grant the degree of precision, ductility, and sensitivity to the context that is typical of human beings’ and many other animals’ sensorimotor coordination. To obtain such sophisticated sensorimotor coordination, it is necessary that a part of those mental states that are already Intentional and subjective from a functional point of view become conscious as well.
Ensuring that a subset of the brain activity becomes conscious (that is, it makes the person who has f-conscious and f-self-conscious perceptions attentive and/or vigilant) is precisely the function of the neuro-modulation symbolically indicated by “nm1” here. This neuro-modulation is largely coincidental with the processes of brain synchronization between oscillating neuronal circuits . Single neuronal processes that have been so synchronized exchange information with each other. In this way, neuronal synchronization brings about the coherence and flexibility of behavior typical of human beings and other animals.
To detail, primary phenomenal consciousness is a self-monitoring activity that the brain applies to other parts of its own activity so as to fine tune the movements of the body with the environment. Therefore, primary phenomenal consciousness is a precondition of the brain coordination activity that has been reconstructed by B. Baars  as “global workspace memory” in cognitive psychological terms and by G. Edelman as the “dynamic core” (see above) in neurological terms. On this basis, the hypothesis can be proposed that primary phenomenal consciousness (that is, attention and/or vigilance) is not a non-physical substance or a non-physical spiritual property, but rather a sort of “machine-code” that operates inside the brain to give the information conveyed by certain parts of brain dynamics the “format” needed to access the global workspace memory.
ᅟA reconstruction of brain activity in the language of neurosciences is comparable to an image presented in text format. That same brain activity is instead comparable to Marilyn’s image if the brain’s internal self-monitoring representation is given in the “format” of consciousness. In other words, the phenomenological gap between having a subjective experience and its systemic brain implementation is indubitable: If I have a toothache, it may be that I know nothing about the neuronal correlates of my pain but I cannot help but feel it! However, it is a mistake to believe that this phenomenological gap can only be explained by the admission of an ontological gap (as dualists think). From an ontological point of view, my pain is not different from its physical implementation, that is, it is not different from a higher order property of brain dynamics. The phenomenological gap between pain and its neuronal correlates can be explained as the result of representing the same thing in two different formats: The former format belongs to the language of neuroscience, the latter to a “machine code” of the brain developed by biological evolution through natural selection .
It will perhaps be objected that by this hypothesis, the explanatory gap between qualia and their neuronal correlates is simply transferred to the “consciousness code” but is not canceled. Why do you perceive the objects whose surface reflects electromagnetic waves having a length between 620 and 750 nm just as red and not, for example, as green or yellow ? The hypothesis that phenomenal consciousness is a kind of brain machine code does not seem to explain any connection between wavelengths and colors and, more generally, between qualia and brain activity. Therefore, you might object that my hypothesis does not solve the “hard problem!”
Well, in a certain sense, this is true. However, this failure has nothing to do with the existence of a metaphysical difference between mind and body as dualists believe: The hypothesis that conscious mental states are identical to higher order properties of brain dynamics does not explain why a certain property of brain activity is identical to a certain color because of the trivial fact that there is nothing to explain! The connection is arbitrary and therefore is not rationally justifiable. It is the result of a sort of convention, that is, of a code blindly introduced by Mother Nature through natural selection in the course of biological evolution to allow the brains that adopt it to build a more accurate and useful image of the external world: an image that contributes to obtaining better sensorimotor coordination by exploiting, for example, the way in which objects reflect light or more generally the way in which certain physical properties excite sense organs and, through them, the brain. There is no phenomenological similarity between the physical properties of brain dynamics and the qualia that they implement. However, thanks to perceiving qualia, human beings and many other animals have a very effective trick at their disposal for reconstructing an image of the external environment that can guide their movements. Obviously, Mother Nature could have found many other tricks to improve the fine tuning of the interaction between animals and their environment. However, once the trick of primary phenomenal consciousness was “found out” by casual mutations and became widespread and stabilized by natural selection, it played and plays a decisive role in determining the behavior of at least human beings and probably all mammals and other animals .
To sum up, in my example of the perception of the fact that the traffic light is red, consciousness appears in its philosophical reconstruction as “primary phenomenal consciousness” (see the adverbial operator “consciously(…)” in (1b)), in its functional reduction as “functional consciousness” (see the adverbial operator “f-consciously(…)” in (2b)), and in its systemic brain implementation as “brain consciousness” (see the neuro-modulation “nm1(…)” in (3b)). If you choose the neurological description as the description that by default must be considered the best representation of reality in a scientific worldview, then, brain consciousness is the only form of consciousness that is truly real and causally effective. Functional consciousness is instead a redescription of brain consciousness in the language of cognitive psychology. Finally, phenomenal consciousness is the “format” that the other two neuro-modulations (“nm2” and “nm3”) assume if they are further neuro-modulated by the machine code “nm1”: by assuming the format of consciousness, “nm2” becomes the sense of agency that accompanies every voluntary action (see the “Ego” as part of the content of my perception: that perception is my perception), “nm3” becomes the object of my perception (see how “redly(f-See)” becomes “See([Red*]”, that is, how “seeing in a certain way” becomes “seeing something”). In conclusion, the key to formulating a physicalist-naturalist solution to the “hard problem” is to consider primary phenomenal consciousness not as a non-physical substance or a non-physical property but as a modality for the self-presentation (by the brain to the brain) of some aspects of brain dynamics in a certain internal format, that is, according to a certain cerebral “machine-code.”
Can this conclusion be extended from the primary consciousness of perceptions and emotions to the “higher order consciousness” that accompanies thoughts and language and is typical of human beings ? There is no reason to exclude this extension. However, this is a problem that I do not touch in this article.
Finally, can I say that the “hard problem” has been solved by my hypothesis? I am very far from asserting this. However, it seems to me that the indicated reductionist strategy at least allows us to dispel the conceptual misconceptions that transform the mind-body problem into an unfathomable mystery.
Compliance with ethical standards
This article does not contain any studies with human participants or animal performed by the author.
Conflict of interest
The author declares that he has no conflict of interest.
It was not necessary to obtain any informed consent by anyone since the article is a philosophical general reflection without any reference to particular persons.
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