Undocumented predicates

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

 act_tree(Arg1, Arg2, Arg3)

 times(Arg1, Arg2, Arg3)

 pac_product(Arg1, Arg2, Arg3, Arg4)

 scons(Arg1, Arg2, Arg3)

 paths_of_term(Arg1, Arg2)