Undocumented predicates

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

 nf(Arg1, Arg2)

 wait_linear(Arg1, Arg2, Arg3)

 nf2term(Arg1, Arg2)

 entailed(Arg1)

 split(Arg1, Arg2, Arg3)

 nf_constant(Arg1, Arg2)

 repair(Arg1, Arg2)

 {Arg1}