#mcd: int int -> int
#máximo común divisor entre x e y positivos
#ej: mcd(18,24)->6, mcd(4,9)->1, mcd(7,7)->7
def mcd(x,y):
    assert type(x)==int and x>0
    assert type(y)==int and y>0
    def _mcd(x,y,divisor):
        if x%divisor==0 and y%divisor==0:
            return divisor
        else:
            return _mcd(x,y,divisor-1)
    return _mcd(x,y,min(x,y))
assert mcd(18,24)==6
assert mcd(4,9)==1
assert mcd(7,7)==7

def mcd(x,y):
    assert type(x)==int and x>0
    assert type(y)==int and y>0
    if x==y:
        return x
    elif x>y:
        return mcd(x-y,y)
    else:
        return mcd(x,y-x)
assert mcd(18,24)==6
assert mcd(4,9)==1
assert mcd(7,7)==7