This is mostly an instance of a class of problem discussed in more depth here: http://www.ocf.berkeley.edu/~wwu/cgi-bin/yabb/YaBB.cgi?board=riddles_hard;action=

This is mostly an instance of a class of problem discussed in more depth here: http://www.ocf.berkeley.edu/~wwu/cgi-bin/yabb/YaBB.cgi?board=riddles_hard;action=display;num=1177584051 http://www.ocf.berkeley.edu/~wwu/cgi-bin/yabb/YaBB.cgi?board... I say mostly because the bit where one switch must be toggled and there are 2 switches makes it a bit different from 23C2. I don't think the difference is useful, though; the set of solutions is probably the same as the solution set for 23C2.