diff --git a/main.py b/main.py
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--- /dev/null
+++ b/main.py
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+from tabulate import tabulate
+
+from numeric.compute import matmul, transpose, rot_2D
+from util.tools import substring
+
+if __name__ == '__main__':
+    # Substring
+    original = "GEEKSFORGEEKS"
+    # print(substring(original, 0, 5))  # Output: GEEKS
+    # print(substring(original, 5))  # Output: FORGEEKS
+
+    # Matrix multiplication
+    matrix_a = [[3, 4, -1, 4],
+                [-2, 2, 5, 1]
+                ]
+    matrix_b = [[1, 3, -2],
+                [2, 5, 1],
+                [-1, 4, -4],
+                [2, 3, 6]
+                ]
+    matrix_c = matmul(matrix_a, matrix_b)
+    # print("Ergebnis C = A * B:")
+
+    # for row in matrix_c:
+    #     print(row)
+
+    # Transposition
+    matrix = [
+        [1, 2, 3],
+        [4, 5, 6]
+    ]
+    # print(tabulate(transpose(matrix)))
+
+    # Rotation
+    print(tabulate(rot_2D(90)))
diff --git a/numeric/__init__.py b/numeric/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/requirements.txt b/requirements.txt
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index 0000000..470d877
Binary files /dev/null and b/requirements.txt differ
diff --git a/util/__init__.py b/util/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/util/tools.py b/util/tools.py
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index 0000000..4e67e39
--- /dev/null
+++ b/util/tools.py
@@ -0,0 +1,21 @@
+def substring(string: str, start: int, end: int = 0) -> str:
+    """
+    A substring function
+    :param string: The string
+    :param start: The starting index
+    :param end: The ending index. If None, this is set to the length of the substring     :return:
+    """
+    if not isinstance(string, str):
+        raise ValueError("No string provided")
+    if not isinstance(start, int):
+        raise ValueError("No starting index provided")
+
+    if end is None:
+        end = len(str)
+
+    result = ""
+
+    for i in range(start, end):
+        result += string[i]
+
+    return result