# MODULO PROPIO
def sumar (n1, n2):
    return n1 + n2

def resta (n1, n2):
    return n1 - n2

def multiplicar (n1, n2):
    return n1 * n2

def dividir (n1, n2):
    if n2 == 0:
        return None
    else:
        return n1 / n2