the joke is the off by one error. 3 instead of 2. Cache invalidation is a true challenge. Naming things is a true challenge too. Same level of complexity (if

the joke is the off by one error. 3 instead of 2. Cache invalidation is a true challenge. Naming things is a true challenge too. Same level of complexity (if not more) as cache invalidation since it deals with psychology of the user/programmer, patterns of thinking, etc.