The purpose of this note is to discuss how various Sobolev spaces defined on
multiple cones behave with respect to density of smooth functions,
interpolation and extension/restriction to/from \RR^n. The analysis
interestingly combines use of Poincar\'e inequalities and of some Hardy type
inequalities.Comment: Modifications following the referee's suggestions. Some typos and
math typos corrected. Addition of references to Poincar\'e inequalities on
sphere