Common Tangents to Spheres in R3

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.

• Type: Journal
• Year: 2006
• Where: DCG
• Authors: Ciprian Borcea, Xavier Goaoc, Sylvain Lazard, Sylvain Petitjean
• Keywords: DCG 2006, Real Common Tangent