Interesting....
acos is integrated using heuristics to choose a suitable substitution. For a=1, the -a^2+1 in the sqrt simplifies to 0, and a different substitution is selected.
We have to think about this.
Rainer
The integral of acos (x-1) is not computed. (tested with psl version built from trunk, revision 1727)
int(acos(x-1),x) returns int(acos(x-1),x)
However
int(acos(x-a),x) returns " - acos( - a + x)*a + acos( - a + x)*x - sqrt( - a^2 + 2*a*x - x^2 + 1).
Interesting....
acos is integrated using heuristics to choose a suitable substitution. For a=1, the -a^2+1 in the sqrt simplifies to 0, and a different substitution is selected.
We have to think about this.
Rainer
I added a committed a fix, by adding a couple of integration rules.
Rainer