Remark identify_Acc_b:
forall x,
Acc (order uf.(m)) x -> repr uf x <> a -> Acc (order (M.set a b uf.(m))) x.
Remark identify_Acc:
forall x,
Acc (order uf.(m)) x -> Acc (order (M.set a b uf.(m))) x.

Lemma identify_wf:
well_founded (order (M.set a b uf.(m))).