add chain branching strategy
add chain to imports
factor debug to onaction and write
onaction imports
add sfilter strategy
Issue 3561: Initial fix
Issue 3561 fixed for +,-,*,/
Changed procedures that deal with exceptions. Fixed error with limit function under the new rules for addition
Removed redundant include. Bug fixed.
Changed  precision to 1 for C.Float._new
Merge branch 'master' of https://github.com/sympy/sympy into issue-3561
Minor changes to already implemented procedured
Kumaraswamy distribution
Raised cosine distribution
U-quadratic distribution
Von Mises distribution
Test args for new distributions
Erlang distribution
Non-central chi distribution
F distribution