Opaque PlusOneMinus'_e.
Definition PlusOneMinus_e : Cobham :=
Comp 2 PlusOneMinus'_e [Proj 2 0; Comp 2 Normalize_e [Proj 2 1] ].

Lemma PlusOneMinus_length : forall l,
length (Sem PlusOneMinus_e [nth 0 l nil; nth 1 l nil]) <= S (length (nth 0 l nil)).