Todo:

• fix constant handling in deriv stoch_exp rule

Undocumented predicates

The following predicates are exported, but not or incorrectly documented.

 max(Arg1, Arg2, Arg3)

 mul(Arg1, Arg2, Arg3)

 add(Arg1, Arg2, Arg3)

 pow(Arg1, Arg2, Arg3)

 exp(Arg1, Arg2)

 llog(Arg1, Arg2)

 log(Arg1, Arg2)

 lse(Arg1, Arg2)

 deriv(Arg1, Arg2, Arg3)

 back(Arg1)

 grad(Arg1)

 esc(Arg1, Arg2, Arg3)

 expand_wsums

 wsum(Arg1, Arg2)

 add_to_wsum(Arg1, Arg2, Arg3)

 gather_ops(Arg1, Arg2, Arg3)