fact: Fixpoint PP_plus (e f:expr) {struct e} : expr := let d := expr_plus e f in match e, f with | expr_plus e1 e2, f => PM_plus (PP_plus e2 f) e1 | expr_int i, f => PM_plus f e | _, _ => d end.
imports: CoRN.logic.CLogic Coq.Bool.Bool