fact: Definition lt_psi a b a' b':= ((a < a') && (b < [a', b'])) || ((a == a') && (b < b')) || ((a' < a) && ([a, b] < b')) || ((a' < a) && ([a, b] == b')).
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat) mathcomp(fintype bigop)