fact: Definition concat s1 s2 := match s1, s2 with | Leaf, _ => s2 | _, Leaf => s1 | _, Node _ l2 x2 r2 => let (s2',m) := remove_min l2 x2 r2 in join s1 m s2' end.
imports: FunInd MSetInterface MSetGenTree BinInt Int