In Go, there is a potentially repetitive sequence of moves called a "ko." So if your opponent takes a ko from you, you have to make a move elsewhere on the board, called a ko threat, before "taking back" the ko, in order to break up the repetition. But suppose someone "repeats" by taking back a ko, without making a ko threat. What are the penalties?
My understanding is that in a tournament, the penalty will be a forfeit of the game. But I've never seen this rule enforced in informal play. The standard "fix" is that the offender is forced to take back his ko "recapture," and make a ko threat.
Is my understanding of the tournament rule correct? And is there an informal "house rule" that prevents the application of this rule in casual games?