diff --git a/Week04/functions_elif_yalvac.py b/Week04/functions_elif_yalvac.py
new file mode 100644
index 00000000..b14e51ce
--- /dev/null
+++ b/Week04/functions_elif_yalvac.py
@@ -0,0 +1,33 @@
+# 1. custom_power
+custom_power = lambda x=0, /, e=1: x ** e
+
+
+
+# 2. custom_equation
+def custom_equation(x: int = 0, y: int = 0, /,
+                    a: int = 1, b: int = 1, *,
+                    c: int = 1) -> float:
+    """
+    Calculates a specific mathematical expression.
+
+    :param x: positional-only integer, default 0
+    :param y: positional-only integer, default 0
+    :param a: positional-or-keyword integer, default 1
+    :param b: positional-or-keyword integer, default 1
+    :param c: keyword-only integer, default 1
+    :return: result of (x**a + y**b) / c as float
+    """
+
+    for val in (x, y, a, b, c):
+        if not isinstance(val, int):
+            raise TypeError("must be int")
+    return (x ** a + y ** b) / c
+
+
+
+# 3. fn_w_counter
+def fn_w_counter() -> (int, dict[str, int]):
+    if not hasattr(fn_w_counter, "count"):
+        fn_w_counter.count = 0
+    fn_w_counter.count += 1
+    return fn_w_counter.count, {__name__.split('.')[-1]: fn_w_counter.count}