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