# For what Recursion is, please check theory/recursion 

# Simple Factorial Python Recursion 
def factorial(n) : 
    if n == 0 : 
        return 1 
    else : 
        return n * factorial(n-1)

# Simple Greatest Common Divisor Recursion 
def gcd(x, y) : 
    if y == 0 : 
        return x 
    else : 
        return gcd(y, x%y)