  We define a natural concept of duality for the h-Hopf algebroids introduced
by Etingof and Varchenko. We prove that the special case of the trigonometric
SL(2) dynamical quantum group is self-dual, and may therefore be viewed as a
deformation both of the function algebra F(SL(2)) and of the enveloping algebra
U(sl(2)). Matrix elements of the self-duality in the Peter-Weyl basis are
6j-symbols; this leads to a new algebraic interpretation of the hexagon
identity or quantum dynamical Yang-Baxter equation for quantum and classical
6j-symbols.
