Remark in_norepet_unique:
  forall id g (gl: list (ident * globdef F V)),
  In (id, g) gl -> list_norepet (map fst gl) ->
  exists gl1 gl2, gl = gl1 ++ (id, g) :: gl2 /\ ~In id (map fst gl2).

Theorem find_def_inversion: forall p b g, find_def (globalenv p) b = Some g -> exists id, In (id, g) (prog_defs p).