I was typing fast and produced this repeatable phenomenon.
f=:%*+-# 5!:4 < 5!:4 < f % * + - # Any string seems to work this way f=: 13 :'x*:y%x' 5!:4 < 5!:4 < f [ *: %~ I would expect either: 5!:4 <'f' -- [ --+- *: L- ~ --- % or 5!:4 <f 5!:4 < f Linda ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm