="Bill Gosper" <billgosper@gmail.com> we still have the problem of naming this solid! Marc LeBrun>tympanon tympanohedron? Note that it's like a pentagonal antiprism (DoD NSA opponent?) but with M-shaped equilateral pentagonal flanks instead of equilateral triangles. We could recognize the (countable) family of "M" antiprisms and call this the pentagonal one. --rwg