I am new to Maxima doing two things - in order of importance
1. Review college algebra I had more than 40 years ago.
It's scratch pad that is more legible than my handwriting and
easier to save.
2. "Solve" a system of equations that are quadratic in x,y,z and
linear in t. Fortunately all x^2, y^2, and z^2 terms cancel ;)
The question.
I get to a point of a simplified set of equations which contain
subexpressions such as
a^2 + b^2 + c^2
I, having defined the problem, recognize that
r^2 = a^2 + b^2 + c^2
Can I have have Maxima recognize a^2 + b^2 + c^2 and substitute r^2 ?
It may appear as -a^2 - b^2 - c^2 , for which I would like to substitute
-r^2 .