Algebra · no timer, no score

Rule Machine

Every machine here runs one rule, and the rule can ask a question. First you read rules and say what they will do. Then somebody changes one, and you work out what they changed.

At the end you are handed a rule that does not do its job, and then one that does its job perfectly — for a job nobody wants any more. Both are yours to fix. Any rule that works is a right answer.