Undocumented predicates

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

 list_sum(Arg1, Arg2)

 list_product(Arg1, Arg2)

 list_lcm(Arg1, Arg2)

 difs(Arg1)

 fold_op(Arg1, Arg2, Arg3, Arg4)

 fold_op(Arg1, Arg2, Arg3)

 maplist_op(Arg1, Arg2, Arg3)

 maplist_op(Arg1, Arg2, Arg3, Arg4)

 maplist_op(Arg1, Arg2, Arg3, Arg4, Arg5)

 maplist_op(Arg1, Arg2, Arg3, Arg4, Arg5, Arg6)

 enumerate(Arg1, Arg2)

 compare_like(Arg1, Arg2, Arg3, Arg4)

 subterms(Arg1, Arg2, Arg3)

 set_knowledge(Arg1, Arg2)

 find_constraint(Arg1, Arg2)

 local_chr(Arg1, Arg2, Arg3)

 function_expansion(Arg1, Arg2, Arg3)

 phrase_from_file_debug(Arg1, Arg2, Arg3)