I heard that advanced expression manipulation isn't Sage's strong side. But are there simple conversions like convert(expr, X) where X is in {factorial, binomial, Gamma, hypergeom, partfrac, etc.. }?
For example how to convert (n!/k!)*binomial(k,n-k) to factorials? With Maple this would look like:
convert( (n!/k!)*binomial(k,n-k), factorial);
