Description: Define the R -coset of A . Exercise 35 of Enderton p. 61. This
is called the equivalence class of A modulo R when R is an
equivalence relation (i.e. when Er R ; see dfer2 ). In this case,
A is a representative (member) of the equivalence class [ A ] R ,
which contains all sets that are equivalent to A . Definition of
Enderton p. 57 uses the notation [ A ] (subscript) R , although
we simply follow the brackets by R since we don't have subscripted
expressions. For an alternate definition, see dfec2 . (Contributed by NM, 23-Jul-1995)