Stavros and Robert
Thank you for these explanations.
Now, the real question. I understand that most commands assume that the global
flag 'simp' is set to 'true', so that in general it is safer to keep it in its
default value. However, in some particular cases, the result of the automatic
simplification on an expression is not what I may want to get. I.e. at some
steps I may like to get higher control of the computation path.
So I wonder how to keep the global 'simp' set to 'true' and preserve the
result of ev(...,simp=false) from the "outer" simplification.
Alejandro Jakubi