  In 2006, Ryu and Takayanagi (RT) pointed out that (with a suitable cutoff)
the entanglement entropy between two complementary regions of an equal-time
surface of a d+1-dimensional conformal field theory on the conformal boundary
of AdS_{d+2} is, when the AdS radius is appropriately related to the parameters
of the CFT, equal to 1/4G times the area of the d-dimensional minimal surface
in the AdS bulk which has the junction of those complementary regions as its
boundary, where G is the bulk Newton constant. We point out here that the
RT-equality implies that, in the quantum theory on the bulk AdS background
which is related to the boundary CFT according to Rehren's 1999 algebraic
holography theorem, the entanglement entropy between two complementary bulk
Rehren wedges is equal to 1/4G times the (suitably cut off) area of their
shared ridge. (This follows because of the geometrical fact that, for
complementary ball-shaped regions, the RT minimal surface is precisely the
shared ridge of the complementary bulk Rehren wedges which correspond, under
Rehren's bulk-wedge to boundary double-cone bijection, to the complementary
boundary double-cones whose bases are the RT complementary balls.) This is
consistent with the Bianchi-Meyers conjecture -- that, in a theory of quantum
gravity, the entanglement entropy, S, between the degrees of freedom of a given
region with those of its complement is S = A/4G (+ lower order terms) -- but
only if the phrase 'degrees of freedom' is replaced by 'matter degrees of
freedom'. It also supports related previous arguments of the author --
consistent with the author's 'matter-gravity entanglement hypothesis' -- that
the AdS/CFT correspondence is actually only a bijection between just the matter
(i.e. non-gravity) sector operators of the bulk and the boundary CFT operators.
