My question is based on Dunnington's biography of Gauss: Gauss: titan of science. In it Dunnington mentions that Gauss, in his response to Janos Bolyai's paper, sent him a synthetic proof of the angular deficit theorem in hyperbolic geometry, and in addition recommended him to find the hyperbolic volume of a tetrahedron in this new geometry.
Also in Dunnington biography, he mentions a note from 1841 by Gauss, again on the volume of the tetrahedron, found among the pages of Lobachevsky's paper.
So what is the importance of the problem, and where are the relevant notes in Gauss's Nachlass?