| (_, _, _, C.Lambda _, []) as config -> config
| (k, e, ens, C.Lambda (_,_,t), p::s) ->
reduce (k+1, (RS.stack_to_env ~reduce ~unwind p)::e, ens, t,s)
| (_, _, _, C.Lambda _, []) as config -> config
| (k, e, ens, C.Lambda (_,_,t), p::s) ->
reduce (k+1, (RS.stack_to_env ~reduce ~unwind p)::e, ens, t,s)