Definition interc (c : coef) :  K :=
fold_left (fun res v => res + ({m[v]}))%f c 0%f.
Notation "{c[ x ]}" := (interc x).

Lemma copp_c c : {c[copp c]} = (-{c[c]})%f.
Definition cscale (v : var) (c : coef) : coef :=
map (term_scale v) c.