  Following Blass, we call a real a ``needed'' for a binary relation R on the
reals if in every R-adequate set we find an element from which a is Turing
computable. We show that every real needed for Cof(N) is hyperarithmetic.
Replacing ``R-adequate'' by ``R-adequate with minimal cardinality'' we get
related notion of being ``weakly needed''. We show that is is consistent that
the two notions do not coincide for the reaping relation. (They coincide in
many models.) We show that not all hyperarithmetical reals are needed for the
reaping relation. This answers some questions asked by Blass at the Oberwolfach
conference in December 1999.
