Select all true statements. If n is not a multiple of 9, then nis not a multiple of 9.
Let the universe U = R. The negation of
Vx, (x2 > 0) → (x > 0) is 3x, (x2 > 0) A (x < 0).
✓ Let U = NU{-1} be the universe. Then the statements
Vx, 3y, xy < 0 and 3x, Vy, xy < 0 are logically equivalent.
Let the universe be V = N. Then the statement
Vk, 3n, nk - 1 = 0 is true.