Text: With a bit of elementary mathematics and a lot of keen insight, Arrow was forced to a sobering  If a reasonable voting system is one that respects unanimity and precludes flip-flops, then there are no reasonable voting systems, with one exception--the system that picks one voter and makes him a dictator.
Entailment: Arrow was forced to a sobering If a reasonable voting system
Contradiction: Arrow wasn't forced to a sobering If a reasonable voting system