> > > I suggest that atan(tan(x)) not simplify unless we know -%pi/2 <x > <%pi/2 > > how about atan(tan(x)) => mod (x + %pi/2, %pi) - %pi/2 ? > I prefer Robert's solution, but agree that it would be nice to have something simpler. Expressions like this appear all the time if you're being careful....