Fix the test failure.
Fix the examples.
Test the examples.
PEP 8 cleanup.
Remove 'import sys' and raise exceptions in the usual way.
Remove ZERO, ONE, etc. and replace by S.Zero, etc.
Docstring cleanup.
Remove duplicated stuff.
Fixed the cartan_matrix doctest
Fix summation(k, (k, 0, oo)) == nan, should be oo
Implement is_positive handler for factorial (partial fix for issue 1072)
Cleanup eval_sum_hyper()
Fix issue 1072
rsolve: simplify substitution of initial values
rsolve_hyper: fix issue 3745 [1/2]

    Return the correct number of arbitrary constants
    and refactor 'symbols' option handling.
rsolve_hyper: fix issue 3745 [2/2]

    Handle the case when the root of the denominator of
    the ratio y(n+1)/y(n) is symbolic: use direct comparison
    instead of max().  See also commit 39dc464 and issue 2408.

    Add test for issue 3745.
Merge pull request #2311 from skirpichev/3745-rsolve_hyper-fix

Fix issue 3745
Merge pull request #2310 from skirpichev/1072-infinite-sums

Fix issue 1072
Merge pull request #2237 from meclark256/liealgebras_1

Lie algebras: Type A
Remove EMPTY, replace by checking len() != 0.