As the reader can easily guess, each issue of this journal is constructed as a result of an extensive debate. The contributors’ voices, expertise and curiosity are different and one of the editors’ tasks lies in finding a balanced variety of the articles: by subject, by level of complexity, by interest for the readers and so on. Then, when the issue is ready, it is good to find that something unexpected has appeared, as often happens, something that goes beyond the expected structure and provides it with a kind of autonomy.

Today, in the issue you have in your hand, you may recognise a motif that, here and there, in different and appropriate forms, seems to have taken over. It is the theme of wonder that accompanies the satisfaction of curiosity.

This feeling is first evoked in the article by Andrea Capozucca, the third instalment in his ongoing series devoted to “Communicating mathematics in Europe”; this time, he discusses the topic with Andrew Jeffrey, who actually is a magician, but is also a teacher who found a link between his main interests: magic and mathematics, to the benefit of his teaching.

Another article demonstrates that mathematical structures are first of all within ourselves. This is not new, of course, but look at the images and follow the discussion in “Matter built, excavated, split: a journey through fractal cities” by Sandra Lucente of the University of Bari, showing how some of these structures—in this case of fractal type—are revealed by the ways—embedded in the rocks, excavated in stone, constructed in dwellings—in which, over the centuries, man has dealt with the morphological features of the terrain and the human problems associated with them.

And then? What else arouses our curiosity in this issue? The paper “Image-matching technology applied to 15th-century printed book illustration” by two young researchers, Matilde Malaspina and Yujie Zhong (both graduate students at the University of Oxford), introduces us to the problems of visual recognition of the illustrations in the incunabula, the precious books printed before 1500: reconstructing the exact composition of the printed sheet makes it possible to shed light on important aspects of these works, such as the transmission of texts, commercial and cultural relations among different printers, technicians, artists, engravers, iconographic traditions, etc. Here too, wonder is linked to the ability to address a problem whose inherent complexity is much greater than that of other categories of images.

Curiosity, magic, wonder. Let us return now to an area that is more usual for mathematics, but no less interesting. In her paper “Earth’s temperature and climate”, Elena Prestini of the University of Rome “Tor Vergata” reminds us of an alarming issue for our generation, climate, which controls the life of our planet, and tells of its mathematical study, starting with Joseph Fourier. Renato Betti—one of the authors of this editorial—tells us in “The twin prime conjecture and other curiosities regarding prime numbers” about a recent result on the fascinating, and in some ways even magical, sequence of prime numbers. In addition to the result, it is the method used that arouses interest, due to the uncertainty of its procedures.

There are two more papers dealing with the application of mathematical methods to problems of life. The first is in a classical spirit: in “The paradox of Vito Volterra’s predator–prey model”, Jean-Marc Ginoux of the University of Toulon covers the fundamentals of population dynamics, from Malthus to the modern approach, via the great contributions by Vito Volterra. Then Tullio Aebischer proposes in “A new algorithm for the rating of orienteering athletes: the OriELO system (OE)” an original method to assign ratings in orienteering competitions, the sport consisting in navigating terrain marked by predefined checkpoints using only a compass and a map; it turns out that the proposed rating method is borrowed from that used by chess players. What does chess have to do with it, you will ask? This too seems to be a bit of mathematical magic.

In conclusion, Pietro Nastasi, historian of mathematics and editor of the journal PRISTEM/Storia. Note di Matematica, Storia, Cultura, reviews La corrispondenza massonica di Luigi Cremona con Giosuè Carducci e Francesco Magni, edited by Aldo Brigaglia and Simonetta Di Sieno, the third volume in a series about Italian mathematicians at the time of the unification of Italy, published by Mimesis. It recounts a piece of modern Italian history that sees, in mid-nineteenth century, the mathematician Luigi Cremona in correspondence with two other well-known intellectuals: poet Giosuè Carducci and physician Francesco Magni.

All that remains now is to wish you, as usual, “enjoy your reading!”.

Translated from the Italian by Daniele A. Gewurz.