let subst env lval exp p =
let mem_here = mem_at env Clabels.Here in
let v, mu = get_var_and_mu mem_here lval exp in
Wp_parameters.debug ~level: 3 "hoare:subst %a <-- %a@."
F.pp_term (F.var v) F.pp_term mu;
D.subst v mu p