(* Test robustness of Groebner tactic in presence of disequalities *)
Require Export Reals.
Require Export Nsatz.
Open Scope R_scope.

Lemma essai :
forall yb xb m1 m2 xa ya,
xa <> xb ->
yb - 2 * m2 * xb = ya - m2 * xa ->
yb - m1 * xb = ya - m1 * xa ->
yb - ya = (2 * xb - xa) * m2 ->
yb - ya = (xb - xa) * m1.