## Abstract

Let *I* and *A* be classes, *F* a functional relation between *I* and *A*. Then *F* is sometimes called a **family of elements of** *A* **indexed by** *I* (or **with** *I* **as index class**) and we write (*F*(*i*))_{i∈I} instead of *F*. In particular, if *E* is a set then a family of elements of **P**(*E*) is called a **family of subsets** of *E* indexed by *I*. If *F* is such a family and we write *X*_{ i } = *F*(*i*) for each element *i* in *I* then we denote the family *F* by (*X*_{ i })_{i∈I}.

## Keywords

Mathematical Logic Identity Mapping Unique Mapping Pairwise Disjoint Projection Mapping
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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## Copyright information

© Springer Science+Business Media New York 1998