There is a gentle and domineering word in the math book: there is only one.

There is a rigorous and firm word in the math book: if and only if.

There is a word in the math book that was struck by lightning: existence and uniqueness.

There is a distant word in the math book: parallel and disjoint.

There is a word in the math book that sounds best: sum.

There is a desperate word in the math book: no solution.

There is a persistent word in the math book: constant establishment.

There is another cruel word in the math book: totally unnecessary.

From then on, I fell in love with mathematics.