current community chat blog Mathematics Mathematics Meta Sign up or log in to customize your list. more stack exchange communities Stack Exchange sign up log in tour help Tour Start here for a quick overview of the site Help Center Detailed answers to any questions you might have Meta Discuss the workings and policies of this site Mathematics Questions Tags Users Badges Unanswered Ask Question Take the 2-minute tour × Mathematics Stack Exchange is a question and answer site for people studying math at any level and professionals in related fields. It's 100% free, no registration required. 1 not equal to 0 stated as a condition, why? up vote 3 down vote favorite In Lindsay Childs' Algebra text (3ed pg 141), it statements this proposition regarding a ring homom...