fact: Definition itv_join i1 i2 : interval T := let: Interval b1l b1r := i1 in let: Interval b2l b2r := i2 in Interval (b1l `&` b2l) (b1r `|` b2r).
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(div fintype bigop order ssralg finset fingroup) mathcomp(ssrnum)