Declare compare() methods
Implement Symbol::compare()
Implement Integer::compare()
Implement Rational::compare()
Implement Sin::compare()
Implement Cos::compare()
Implement Pow::compare()
Update the comment
Implement Add::compare()
Implement Mul::compare()
Implement map_basic_basic_compare()
Add a test for compare()
Implement Basic::__cmp__()
Add a test for __cmp__()
Add another test, fix a bug
Add another test, fix a bug
Add a test, fix a bug
Fix few more bugs
Add few tests for Add
Add: use map_basic_int (equivalent, but simpler)