The pentagonal cupola consists of 5 equilateral triangles, 5 squares, 1 pentagon, and 1 decagon. In geometry, a decagon is a ten-sided polygon or 10-gon. A "skew zig-zag decagon" has vertices alternating between two parallel planes. A regular skew decagon is vertex-transitive with equal edge lengths. A similar gold lozenge from Clandon Barrow, in Dorset, used a decagon in its design. The choir was closed with a semi-circular apse, which was encased within a half decagon. The layout is that of a decagon with an octagonal drum. A regular triangle, decagon, and pentadecagon can completely fill a plane vertex. The interior of such an decagon is not generally defined. Need to search on "decagon" hexadecagon, etc. The "regular decagon" has Dih symmetry, order 20. The roomy hall has a choir end with five sides of a decagon. A regular icosagram, {20/9}, can be seen as a quasitruncated decagon, t{10/9}={20/9}. The League uses a unique ten-sided (decagon) cage for their events. Gracie returned to the WSOF decagon on July 5, 2014 at , facing Dustin Holyko.