What is the opposite of log_expand

edit

Yes, log_simplify:

sage: e = log(x*y) ; e
log(x*y)
sage: f = e.log_expand() ; f
log(x) + log(y)
sage: f.log_simplify()
log(x*y)

Note that given an sage object e, you can see all methods that can be applied to it, by typing e.<TAB_BUTTON>, and the methods that start with blah by typing e.blah<TAB_BUTTON>, in particular, you could discover both methods by typing:

sage: e.log<TAB_BUTTON>