indexed objects like (a+b).i -> a.i + b.i
* Renamed get_indices() to get_free_indices(), which no longer returns
dummy indices and checks the consistency of indices in sums.
+* sqrfree() factorization fixed and improved syntactically.
* subs() works on matrices.
+* Fixed memory leak in expand().
0.7.3 (28 February 2001)
* Several bugfixes and minor performance tunings.