# only one level nested closure is implemented

def f0(a, b):
    def f1():
        return a + b
    return f1

a = f0(1, 2)
b = f0(3, 4)
assert a() == 3
assert b() == 7


def f0(a, b):
    def f1():
        a = 5   # use this first
        return a + b
    return f1

a = f0(1, 2)
assert a() == 7

def f3(x, y):
    return lambda z: x + y + z

a = f3(1, 2)
assert a(3) == 6

# closure ex
def f(n):
    def g(x):
        if x==n:
            return n
        return g(x+1)
    return g(0)

assert f(10) == 10