problems with integration

[parisse]

Actually the right definition of y3 should be
y3:=y1 -(x-> 48.9047619048*x)
or
y3:=unapply(y1(x) - 48.9047619048*x,x)
unless you want to see y3 modified if y1 is modified.
I have fixed the crash in source. Indeed an infinite recursion while trying to evaluate a mixed function/expression. It was not a very good idea to add code to evaluate expressions like if they are function...