Question
Consider the binary operation $^*$ and o defined by the following tables on set $S = {a, b, c, d}.$
| $o$ | $a$ | $b$ | $c$ | $d$ |
| $a$ | $a$ | $a$ | $a$ | $a$ |
| $b$ | $a$ | $b$ | $c$ | $d$ |
| $c$ | $a$ | $c$ | $d$ | $b$ |
| $d$ | $a$ | $d$ | $b$ | $c$ |