generalize (natc_correct (tvarn v) (tvarn v)); case natc; auto.
intros H; contradict H; auto with arith.
intros H; contradict H; auto with arith.
Qed.
(* Proof *)
Variable interv : tvar -> point K.
Notation "{v[ x ]}" := (interv x).
(* Implementation of variable *)
Variable var : Type.
(* Implementation of coef *)
Variable coef : Type.
Variable cadd : coef -> coef -> coef.
Variable czerop : coef -> bool.
Variable czero : coef.
Variable conep : coef -> bool.
Variable cone : coef.
Variable copp : coef -> coef.
Variable cscale : var -> coef -> coef.
Variable interk : var -> K.
Notation "{k[ x ]}" := (interk x).
Variable interc : coef -> K.
Notation "{c[ x ]}" := (interc x).
Hypothesis cadd_c : forall x y, {c[cadd x y]} = ({c[x]} + {c[y]})%f.
Hypothesis cone_c : {c[cone]} = (1)%f.
Hypothesis conep_c : forall x,
if conep x then {c[x]} = (1)%f else True.
Hypothesis czero_c : {c[czero]} = (0)%f.
Hypothesis cscale_c : forall k x,
{c[cscale k x]} = ({k[k]} * {c[x]})%f.
Hypothesis czerop_c : forall x,
if czerop x then {c[x]} = (0)%f else True.
Hypothesis copp_c : forall x, {c[copp x]} = (- {c[x]})%f.
(* We want to reduce expression *)
Inductive tuple := Tuple (_ _ _: tvar).
Let  line := list tuple.
Let  expr := list (coef * line).
Definition intert (t : tuple) :=
let (p1,p2,p3) := t in '[{v[p1]},{v[p2]},{v[p3]}].
Notation "{t[ x ]}" := (intert x).
Fixpoint interl (l :line) :=
match l with nil => 1%f | t ::l1 => ({t[t]} * interl l1)%f end.
Notation "{l[ x ]}" := (interl x).
Fixpoint intere (e :expr) :=
match e with nil => 0%f | (c,l)::e1 =>
({c[c]} * {l[l]} + intere e1)%f
end.
Notation "{e[ x ]}" := (intere x).
Fixpoint intere1 (e :expr) :=
match e with nil => 0%f | (c,t ::nil)::nil =>
if conep c then {t[t]} else intere e
| _ => intere e end.
Notation "{e1[ x ]}" := (intere1 x).

Lemma intere1_c e : {e1[e]} = {e[e]}.
Inductive sign := Sm1 | S0 | S1.