fact: Definition mcover (s1 s2 : {set M}) := [&& s1 \in mflats, s2 \in mflats, s2 \proper s1 & [forall s, [&& s \in mflats, s2 \subset s & s \subset s1] ==> ((s == s1) || (s == s2))]].
imports: mathcomp(all_ssreflect)