(ii) On Q, * is defined by a * b = ab + 1.

It is known that:

ab = ba mnForE; a, b ∈ Q

⇒ ab + 1 = ba + 1 mnForE; a, b ∈ Q

⇒ a * b = a * b mnForE; a, b ∈ Q

Therefore, the operation * is commutative.

In the above lines, what does "mnForE;" stand for?