diff --git a/Recursion/P29_23_GCD.cpp b/Recursion/P29_23_GCD.cpp
index 604782e..c14cf44 100644
--- a/Recursion/P29_23_GCD.cpp
+++ b/Recursion/P29_23_GCD.cpp
@@ -1 +1,20 @@
 #include <iostream>
+#include <cmath>
+using namespace std;
+
+int gcd(int x, int y){
+	x = abs(x);
+	y = abs(y);
+	if(y == 0)
+		return x;
+	if(y > 0)
+		return gcd(y, x % y);
+	return 0;
+}
+
+int main(){
+	cout << gcd(20 ,30) << endl;
+	cout << gcd(112, 42) << endl;
+	cout << gcd(-112,42) << endl;
+	return 0;
+}
diff --git a/Recursion/P29_23_GCD.exe b/Recursion/P29_23_GCD.exe
new file mode 100644
index 0000000..5d8f6a3
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diff --git a/Recursion/P29_24_checkfunc.cpp b/Recursion/P29_24_checkfunc.cpp
new file mode 100644
index 0000000..843da0c
--- /dev/null
+++ b/Recursion/P29_24_checkfunc.cpp
@@ -0,0 +1,33 @@
+/*
+Request: Code a template module to check if x is in a[0:n-1]
+*/
+
+#include <iostream>
+#include <string>
+using namespace std;
+
+template <class T>
+bool chk(T x, T* a, int n){
+	if(n > 1 && x != a[n - 1])
+		return chk(x,a,n-1);
+	if(n == 1 && x != a[0])
+		return false;
+	return true;
+}
+
+int main(){
+	int a[] = {2,3,4,5,6,7,9};
+	cout << chk(2,a,7) << " " << chk(1,a,7)<<endl;
+	return 0;
+}
+
+/*
+AI wrote like this:
+
+template <class T>
+bool chk(T x, T* a, int n) {
+    if (n <= 0) return false;
+    if (a[n - 1] == x) return true;
+    return chk(x, a, n - 1);
+}
+*/
diff --git a/Recursion/P29_24_checkfunc.exe b/Recursion/P29_24_checkfunc.exe
new file mode 100644
index 0000000..adb0b3d
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