Section RENUMBER.
Variable f: PTree.t positive.
Hypothesis f_inj: forall x1 x2 y, f!x1 = Some y -> f!x2 = Some y -> x1 = x2.

Lemma renum_cfg_nodes:
forall c x y i,
c!x = Some i -> f!x = Some y -> (renum_cfg f c)!y = Some(renum_instr f i).