  We identify a notion of reducibility between predicates, called instance
reducibility, which commonly appears in reverse constructive mathematics. The
notion can be generally used to compare and classify various principles studied
in reverse constructive mathematics (formal Church's thesis, Brouwer's
Continuity principle and Fan theorem, Excluded middle, Limited principle,
Function choice, Markov's principle, etc.). We show that the instance degrees
form a frame, i.e., a complete lattice in which finite infima distribute over
set-indexed suprema. They turn out to be equivalent to the frame of upper sets
of truth values, ordered by the reverse Smyth partial order. We study the
overall structure of the lattice: the subobject classifier embeds into the
lattice in two different ways, one monotone and the other antimonotone, and the
$\lnot\lnot$-dense degrees coincide with those that are reducible to the degree
of Excluded middle.
  We give an explicit formulation of instance degrees in a relative
realizability topos, and call these extended Weihrauch degrees, because in
Kleene-Vesley realizability the $\lnot\lnot$-dense modest instance degrees
correspond precisely to Weihrauch degrees. The extended degrees improve the
structure of Weihrauch degrees by equipping them with computable infima and
suprema, an implication, the ability to control access to parameters and
computation of results, and by generally widening the scope of Weihrauch
reducibility.
