Thanks,
Jan is right: changing to (require (except-in racket/control set)) is dispensing with the problem. Still this is a Racket pitfall close to be a bug imho. Btw. there were more slips in my hastily reduction. In fact, '·indices should search indices, but therefore the last argument to 'filter has to be (range (length L)), not L. Cheers, Joost ____________________ Racket Users list: http://lists.racket-lang.org/users
