fact: Fixpoint Fcons0 (e:PExpr C) (l:list (PExpr C)) {struct l} : list (PExpr C) := match l with nil => cons e nil | cons a l1 => if Peq ceqb (Nnorm O nil e) (Nnorm O nil a) then l else cons a (Fcons0 e l1) end.
imports: ZArith_base