For unions of linear simplicial meshes you can just turn eachpolyhedron into more simplices; not a great idea if it was going to
effect basis conditioning but just fine if it's only used for
But that's not even the real tricky case: For unions of higher order
simplices (or *any*-order hexes/prisms/pyramids) the geometric union
can include *lenses* and even nastier shapes; I can't even imagine the
right way to handle that.