Consider these relations on the set of integers:
R1 = {(a, b) | a ≤ b},
R2 = {(a, b) | a > b},
R3 = {(a, b) | a = b or a = −b},
R4 = {(a, b) | a = b},
R5 = {(a, b) | a = b + 1},
R6 = {(a, b) | a + b ≤ 3}.
Which of these relations contain each of the pairs (3, -3)