We prove that four spheres in R3 have infinitely many real common tangents if and only if they have aligned centers and at least one real common tangent.
We establish upper and lower bounds on the number of connected components of lines tangent to four triangles in R3 . We show that four triangles in R3 may admit at least 88 tangent...
We consider "swept regions" and "swept hypersurfaces"B in Rn+1 (and especially R3) which are a disjoint union of subspaces t = t or Bt = Bt obtained from a va...