Thank you for the pointer to your paper "Getting Started with Lattice Graphics" -- it looks very useful.
I think we're talking past each other on the question of the semantics of formula operators, and it's probably not productive to continue. I would guess that the underlying issue is that we come from different communities, and so have different background assumptions. Perhaps it's the old MIT vs New Jersey story (http://www.jwz.org/doc/worse-is-better.html) -- after all, S/R does come out of the Bell Labs community, and I was in the MIT Lisp community many decades ago.... -s ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.