diff --git a/up_tamer/converter.py b/up_tamer/converter.py
index d31e835..055a4ff 100644
--- a/up_tamer/converter.py
+++ b/up_tamer/converter.py
@@ -142,8 +142,11 @@ def walk_int_constant(self, expression: 'FNode',
 
     def walk_plus(self, expression: 'FNode',
                   args: List[pytamer.tamer_expr]) -> pytamer.tamer_expr:
-        assert len(args) == 2
-        return pytamer.tamer_expr_make_plus(self._env, args[0], args[1])
+        assert len(args) > 0
+        res = args[0]
+        for i in range(1, len(args)):
+            res = pytamer.tamer_expr_make_plus(self._env, res, args[i])
+        return res
 
     def walk_minus(self, expression: 'FNode',
                    args: List[pytamer.tamer_expr]) -> pytamer.tamer_expr:
@@ -152,8 +155,11 @@ def walk_minus(self, expression: 'FNode',
 
     def walk_times(self, expression: 'FNode',
                    args: List[pytamer.tamer_expr]) -> pytamer.tamer_expr:
-        assert len(args) == 2
-        return pytamer.tamer_expr_make_times(self._env, args[0], args[1])
+        assert len(args) > 0
+        res = args[0]
+        for i in range(1, len(args)):
+            res = pytamer.tamer_expr_make_times(self._env, res, args[i])
+        return res
 
     def walk_div(self, expression: 'FNode',
                  args: List[pytamer.tamer_expr]) -> pytamer.tamer_expr:
diff --git a/up_tamer/engine.py b/up_tamer/engine.py
index 0cb7f84..e3a0976 100644
--- a/up_tamer/engine.py
+++ b/up_tamer/engine.py
@@ -404,9 +404,17 @@ def _convert_action(self, problem: 'up.model.Problem', action: 'up.model.Action'
                     expressions.append(expr)
             for t, le in action.effects.items():
                 for e in le:
-                    assert not e.is_conditional() and e.is_assignment()
-                    ass = pytamer.tamer_expr_make_assign(self._env, converter.convert(e.fluent),
-                                                         converter.convert(e.value))
+                    assert not e.is_conditional()
+                    if e.is_assignment():
+                        ass = pytamer.tamer_expr_make_assign(self._env, converter.convert(e.fluent), converter.convert(e.value))
+                    elif e.is_increase():
+                        val = pytamer.tamer_expr_make_plus(self._env, converter.convert(e.fluent), converter.convert(e.value))
+                        ass = pytamer.tamer_expr_make_assign(self._env, converter.convert(e.fluent), val)
+                    elif e.is_decrease():
+                        val = pytamer.tamer_expr_make_minus(self._env, converter.convert(e.fluent), converter.convert(e.value))
+                        ass = pytamer.tamer_expr_make_assign(self._env, converter.convert(e.fluent), val)
+                    else:
+                        raise NotImplementedError
                     expr = pytamer.tamer_expr_make_temporal_expression(self._env,
                                                                        self._convert_timing(t),
                                                                        ass)