from typing import List

def det2x2(llist: List[List[int]])->int:
    assert len(llist) == 2 and len(llist[0]) == 2, "Matrix is not 2x2"
    z = list(zip(llist[0], llist[1][::-1]))
    det = z[0][0]*z[0][1] - z[1][0]*z[1][1]
    return det