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 shift_symbol_address: forall ge id ofs delta, symbol_address ge id (Ptrofs.add ofs delta) = Val.offset_ptr (symbol_address ge id ofs) delta.