Commit 2020-07-06 16:58 f06e4e00
View on Github →feat(data/sym2) Defining the symmetric square (unordered pairs) (#3264)
This adds a type for the symmetric square of a type, which is the quotient of the cartesian square by permutations. These are also known as unordered pairs.
Additionally, this provides some definitions and lemmas for equalities, functoriality, membership, and a relationship between symmetric relations and terms of the symmetric square.
I preferred sym2
over unordered_pairs
out of a combination of familiarity and brevity, but I could go either way for naming.