ONE night some twenty years ago, during a siege of mumps in our enormous family, my youngest sister, Franny, was moved, crib and all, into the ostensibly germ-free room I shared with my eldest brother ...

A prism is a 3D shape which has a constant cross section - both ends of the solid are the same shape and anywhere you cut parallel to these ends will give you the same shape. For example, in the prism ...