Somebody asked me to do something that was partially solved by tsort, but the next step exceeds the limitations of tsort. After a bit of thought I realize this problem was a poster child application for languages like Prolog or Mercury. But I know I'm not going to have to time to learn them. But ruby is pretty flexible... Anybody have any Prolog alike goal finding / backtracking type ruby module available? (Couldn't spot any on RAA or rubyforge.) John Carter Phone : (64)(3) 358 6639 Tait Electronics Fax : (64)(3) 359 4632 PO Box 1645 Christchurch Email : john.carter / tait.co.nz New Zealand A Million Monkeys can inflict worse things than just Shakespeare on your system.