Incidentally, When We're Faced With A "prove Or Disprove," We're Usually Better Off Trying First To Disprove With A Counterexample, For Two Reasons: A Disproof Is Potentially Easier (we Need Just One Counterexample); And Nitpicking Arouses Our Creative Juices. Even If The Given Assertion Is True, Our Search For A Counterexample Often Leads To A Proof, As Soon As We See Why A Counterexample Is Impossible. Besides, It's Healthy To Be Skeptical.