fact: Definition invariant (f : R -> R) (p : ptree piece) := all (fun r => match r with Piece uf vf i => valid f uf vf i end) (ptree_to_list p) /\ exists qh, exists qt, permut (ptree_to_list p) (qh :: qt) /\ invariant_aux qh qt IBu.
imports: Coq(BinPos Reals List) Coquelicot(Coquelicot) Coquelicot Xreal Interval Priority