Using the definitions and propositions discussed so far, complete the first part of the proof of Proposition 2.16(i). Notice that the proofs of Proposition 2.16(i) and (ii) involve constructing proofs by contradiction. Such proofs are also called indirect proofs. This mode of reasoning might look weird, but it is actually quite common in mathematics, science, and everyday thinking. For example, when mathematicians prove that √2 is an irrational number, they can proceed by assuming (for a proof by contradiction) that √2 is a rational number (meaning that √2 can be expressed as a fraction p/q of natural numbers p and q) and then use this assumption to derive a contradiction.