# Some relations are given as  $R_1$ = {(a, b), (b, c), (a, c), (c, b)}  $R_2$ = {(1, 2), (2, 5), (6, 6), (3, 4)}  $R_3$ = {a, p), (b, q), (p, t), (r, t)}  $R_4$ = {(10, 11), (11, 12), (10, 13)}  $R_5$ = {(15, 20), (20, 25), (25, 30)} Which of the given relations are not functions?

$R_1\: and \: R_4$