diff --git a/planning.py b/planning.py
index d9a152e9a..e31cd2f87 100644
--- a/planning.py
+++ b/planning.py
@@ -17,20 +17,25 @@ class PDDL:
 
     def __init__(self, init, goals, actions):
         self.init = self.convert(init)
-        self.goals = expr(goals)
+        self.goals = self.convert(goals)
         self.actions = actions
 
-    def convert(self, init):
+    def convert(self, clauses):
         """Converts strings into exprs"""
+        if not isinstance(clauses, Expr):
+            if len(clauses) > 0:
+                clauses = expr(clauses)
+            else:
+                clauses = []
         try:
-            init = conjuncts(expr(init))
+            clauses = conjuncts(clauses)
         except AttributeError:
-            init = expr(init)
-        return init
+            clauses = clauses
+        return clauses
 
     def goal_test(self):
         """Checks if the goals have been reached"""
-        return all(goal in self.init for goal in conjuncts(self.goals))
+        return all(goal in self.init for goal in self.goals)
 
     def act(self, action):
         """
@@ -61,34 +66,35 @@ class Action:
     """
 
     def __init__(self, action, precond, effect):
-        action = expr(action)
+        if isinstance(action, str):
+            action = expr(action)
         self.name = action.op
         self.args = action.args
-        self.precond, self.effect = self.convert(precond, effect)
+        self.precond = self.convert(precond)
+        self.effect = self.convert(effect)
 
     def __call__(self, kb, args):
         return self.act(kb, args)
 
-    def convert(self, precond, effect):
+    def convert(self, clauses):
         """Converts strings into Exprs"""
+        if isinstance(clauses, Expr):
+            clauses = conjuncts(clauses)
+            for i in range(len(clauses)):
+                if clauses[i].op == '~':
+                    clauses[i] = expr('Not' + str(clauses[i].args[0]))
 
-        precond = precond.replace('~', 'Not')
-        if len(precond) > 0:
-            precond = expr(precond)
-        effect = effect.replace('~', 'Not')
-        if len(effect) > 0:
-            effect = expr(effect)
+        elif isinstance(clauses, str):
+            clauses = clauses.replace('~', 'Not')
+            if len(clauses) > 0:
+                clauses = expr(clauses)
 
-        try:
-            precond = conjuncts(precond)
-        except AttributeError:
-            pass
-        try:
-            effect = conjuncts(effect)
-        except AttributeError:
-            pass
+            try:
+                clauses = conjuncts(clauses)
+            except AttributeError:
+                pass
 
-        return precond, effect
+        return clauses
 
     def substitute(self, e, args):
         """Replaces variables in expression with their respective Propositional symbol"""
@@ -138,10 +144,10 @@ def act(self, kb, args):
 def air_cargo():
     """Air cargo problem"""
 
-    return PDDL(init='At(C1, SFO) & At(C2, JFK) & At(P1, SFO) & At(P2, JFK) & Cargo(C1) & Cargo(C2) & Plane(P1) & Plane(P2) & Airport(SFO) & Airport(JFK)',
+    return PDDL(init='At(C1, SFO) & At(C2, JFK) & At(P1, SFO) & At(P2, JFK) & Cargo(C1) & Cargo(C2) & Plane(P1) & Plane(P2) & Airport(SFO) & Airport(JFK)', 
                 goals='At(C1, JFK) & At(C2, SFO)', 
                 actions=[Action('Load(c, p, a)', 
-                                precond='At(c, a) & At(p, a) & Cargo(c) & Plane(p) & Airport(a)', 
+                                precond='At(c, a) & At(p, a) & Cargo(c) & Plane(p) & Airport(a)',
                                 effect='In(c, p) & ~At(c, a)'),
                          Action('Unload(c, p, a)',
                                 precond='In(c, p) & At(p, a) & Cargo(c) & Plane(p) & Airport(a)',
@@ -207,6 +213,25 @@ def shopping_problem():
                                 effect='At(y) & ~At(x)')])
 
 
+def socks_and_shoes():
+    """Socks and shoes problem"""
+
+    return PDDL(init='',
+                goals='RightShoeOn & LeftShoeOn',
+                actions=[Action('RightShoe',
+                                precond='RightSockOn',
+                                effect='RightShoeOn'),
+                        Action('RightSock',
+                                precond='',
+                                effect='RightSockOn'),
+                        Action('LeftShoe',
+                                precond='LeftSockOn',
+                                effect='LeftShoeOn'),
+                        Action('LeftSock',
+                                precond='',
+                                effect='LeftSockOn')])
+
+
 class Level:
     """
     Contains the state of the planning problem
@@ -559,6 +584,26 @@ def goal_test(kb, goals):
             return None
 
 
+def socks_and_shoes_graphplan():
+    pddl = socks_and_shoes()
+    graphplan = GraphPlan(pddl)
+
+    def goal_test(kb, goals):
+        return all(kb.ask(q) is not False for q in goals)
+
+    goals = expr('RightShoeOn, LeftShoeOn')
+
+    while True:
+        if (goal_test(graphplan.graph.levels[-1].kb, goals) and graphplan.graph.non_mutex_goals(goals, -1)):
+            solution = graphplan.extract_solution(goals, -1)
+            if solution:
+                return solution
+
+        graphplan.graph.expand_graph()
+        if len(graphplan.graph.levels) >= 2 and graphplan.check_leveloff():
+            return None
+
+
 def linearize(solution):
     """Converts a level-ordered solution into a linear solution"""