changes
changes
Revert "changes"

This reverts commit 9f144fb29ce578e776b501ac3dd5430938094ca1.
Revert "Revert "changes""

This reverts commit 84c0d6cefcd2b6b0c9394999fa730a826bccc050.
Revert "changes"

This reverts commit ce524fe2b272280a4636f45ea11712c3de553bfb.
This PR solves the following:

 -> Avoids unneccesary coversions of polynomials to expressions
    which eliminates the cause of most of the unification errors
 -> Adds more tests to recognize_derivative in risch.py