- op(0) of an idx object returns the index value; a nice side-effect of
this is that idx'es no longer all have the same hash value
gamma~0 in p.mu*gamma~mu should be p.0 but is returned as 0
- using coeff(), tcoeff(), lcoeff() or collect() on elements of
noncommutative products might return wrong or surprising results
+* Likewise, subs() can be used to substitute functions, tensors and indexed
+ expressions.
* Added preliminary (re)implementations of color and clifford classes.
* simplify_indexed(): contraction of symmetric and antisymmetric tensors
is zero.