Bloch–Wigner function

Summary

The Bloch–Wigner function $D$ is a real-valued function on the complex plane built from the imaginary part of the dilogarithm and a logarithm correction. Unlike the dilogarithm, it is single-valued and continuous on all of $\C$. It satisfies a clean five-term relation and gives the volume of an ideal tetrahedron in hyperbolic space. This makes it central in hyperbolic geometry and in the theory of the Bloch group.