Headaches are one effect that can come from inhalation of isopropyl alcohol. Isopropyl alcohol, or rubbing alcohol, is often used in the home or in medical facilities to treat various conditions or to sterilize instruments and skin. However, if isopropyl alcohol is inhaled there can be serious side effects.
1a) Definition of contradiction: A contradiction exists any time a proposition P is asserted to be true in conjunction with its negation, not-P. 1b) Definition of conjunction: A conjunction is a connective that joins two propositions.
This alternative proof can be generalised to show that $\sqrt{n}$ is irrational when $n$ is not a square number. Proving something by contradiction can be a very nice method when it works, and there are many proofs in mathematics made easier or, indeed, possible by it.