Let A = {–2, –1, 0, 1}, B = {1, 2, 3, 4} and ‘f’ is a subset of A × B, given by f = {(x, y) | x + y =1}. Is ‘f’ a function from ‘A’ to ‘B’? If not, remove minimum number of elements from the set ‘A’, so that ‘f’ may be a function from the new set to ‘B’.