diff --git a/pyreason/scripts/annotation_functions/annotation_functions.py b/pyreason/scripts/annotation_functions/annotation_functions.py
index 75eb9b6f..e928910d 100755
--- a/pyreason/scripts/annotation_functions/annotation_functions.py
+++ b/pyreason/scripts/annotation_functions/annotation_functions.py
@@ -3,8 +3,6 @@
 import numba
 import numpy as np
 
-import pyreason.scripts.numba_wrapper.numba_types.interval_type as interval
-
 @numba.njit
 def _get_weighted_sum(annotations, weights, mode='lower'):
     """
@@ -49,7 +47,7 @@ def average(annotations, weights):
 
     lower, upper = _check_bound(avg_lower, avg_upper)
 
-    return interval.closed(lower, upper)
+    return (lower, upper)
 
 @numba.njit
 def average_lower(annotations, weights):
@@ -67,7 +65,7 @@ def average_lower(annotations, weights):
 
     lower, upper = _check_bound(avg_lower, max_upper)
 
-    return interval.closed(lower, upper)
+    return (lower, upper)
 
 @numba.njit
 def maximum(annotations, weights):
@@ -82,7 +80,7 @@ def maximum(annotations, weights):
 
     lower, upper = _check_bound(max_lower, max_upper)
 
-    return interval.closed(lower, upper)
+    return (lower, upper)
 
 
 @numba.njit
@@ -98,4 +96,4 @@ def minimum(annotations, weights):
 
     lower, upper = _check_bound(min_lower, min_upper)
 
-    return interval.closed(lower, upper)
+    return (lower, upper)
diff --git a/pyreason/scripts/interval/interval.py b/pyreason/scripts/interval/interval.py
index 18d25ede..66b7bc11 100755
--- a/pyreason/scripts/interval/interval.py
+++ b/pyreason/scripts/interval/interval.py
@@ -4,8 +4,12 @@
 
 
 class Interval(structref.StructRefProxy):
-    def __new__(cls, lower, upper, s=False):
-        return structref.StructRefProxy.__new__(cls, lower, upper, s, lower, upper)
+    def __new__(cls, lower, upper, s=False, prev_l=None, prev_u=None):
+        if prev_l is None:
+            prev_l = lower
+        if prev_u is None:
+            prev_u = upper
+        return structref.StructRefProxy.__new__(cls, lower, upper, s, prev_l, prev_u)
 
     @property
     @njit
diff --git a/tests/unit/disable_jit/test_annotation_functions.py b/tests/unit/disable_jit/test_annotation_functions.py
index fcb94c0b..ac887827 100644
--- a/tests/unit/disable_jit/test_annotation_functions.py
+++ b/tests/unit/disable_jit/test_annotation_functions.py
@@ -4,8 +4,6 @@
 
 import pyreason.scripts.annotation_functions.annotation_functions as af
 
-af.interval = SimpleNamespace(closed=lambda l, u, static=False: SimpleNamespace(lower=l, upper=u))
-
 def _interval(lower, upper):
     return SimpleNamespace(lower=lower, upper=upper)
 
@@ -42,23 +40,27 @@ def test_check_bound(lower, upper, expected):
 def test_average():
     annotations, weights = _example_annotations()
     result = af.average(annotations, weights)
-    assert result.lower == pytest.approx(1.4 / 3)
-    assert result.upper == pytest.approx(0.6)
+    assert isinstance(result, tuple), f"expected tuple, got {type(result)}"
+    assert result[0] == pytest.approx(1.4 / 3)
+    assert result[1] == pytest.approx(0.6)
 
 def test_average_lower():
     annotations, weights = _example_annotations()
     result = af.average_lower(annotations, weights)
-    assert result.lower == pytest.approx(1.4 / 3)
-    assert result.upper == pytest.approx(0.6)
+    assert isinstance(result, tuple), f"expected tuple, got {type(result)}"
+    assert result[0] == pytest.approx(1.4 / 3)
+    assert result[1] == pytest.approx(0.6)
 
 def test_maximum():
     annotations, weights = _example_annotations()
     result = af.maximum(annotations, weights)
-    assert result.lower == pytest.approx(1.0)
-    assert result.upper == pytest.approx(1.0)
+    assert isinstance(result, tuple), f"expected tuple, got {type(result)}"
+    assert result[0] == pytest.approx(1.0)
+    assert result[1] == pytest.approx(1.0)
 
 def test_minimum():
     annotations, weights = _example_annotations()
     result = af.minimum(annotations, weights)
-    assert result.lower == pytest.approx(0.4)
-    assert result.upper == pytest.approx(0.6)
+    assert isinstance(result, tuple), f"expected tuple, got {type(result)}"
+    assert result[0] == pytest.approx(0.4)
+    assert result[1] == pytest.approx(0.6)