let labels_assert_before s = function
| LogicLabel (None, "Pre") -> Logic_const.pre_label
| LogicLabel (None, "Here") -> Clabels.mk_logic_label s
| LogicLabel (Some s, _) -> Clabels.mk_logic_label s
| StmtLabel rs -> Clabels.mk_logic_label !rs
| l -> raise (LabelError l)