diff --git a/src/Solver.ml b/src/Solver.ml
index 69e45db..280e79e 100644
--- a/src/Solver.ml
+++ b/src/Solver.ml
@@ -66,13 +66,13 @@ module Make (T : Utils.Functor) = struct
           begin match (evalc c) with
           | NRet a -> NRet (fun ctx -> (f (a ctx)))
           | NErr e -> NErr e
-          | NDo act -> Utils.not_yet "NDo" (act)
+          | NDo act -> NDo (T.map (fun c -> Constraint.Map(c,f)) act)
           end
       | MapErr(c, f) ->
           begin match (evalc c) with
           | NRet a -> NRet a
           | NErr e -> NErr (f e)
-          | NDo act -> Utils.not_yet "NDo" (act)
+          | NDo act -> NDo (T.map (fun c -> Constraint.MapErr(c,f)) act)
           end
       | Conj(c,d) -> 
           begin match (evalc c) with
@@ -80,10 +80,10 @@ module Make (T : Utils.Functor) = struct
             begin match (evalc d) with
             | NRet b -> NRet (fun ctx -> (a ctx,b ctx))
             | NErr e -> NErr e
-            | NDo act -> Utils.not_yet "NDo" (act)
+            | NDo act2 -> NDo (T.map (fun d -> Constraint.Conj(c,d)) act2)
             end
           | NErr e -> NErr e
-          | NDo act -> Utils.not_yet "NDo" (act)
+          | NDo act1 -> NDo (T.map (fun c -> Constraint.Conj(c,d)) act1)
           end
       | Eq(x,y) -> 
           begin match (Unif.unify (!env) x y) with