MathOverflow is a question and answer site for professional mathematicians. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

I am thinking about the question that: if we double a hyperbolic 3 manifold along its boundary, will the rank of fundemental group of the resulting closed manifold be strictly larger than before?\ The answer is "Yes" if the following question is true. Does every hyperbolic 3 manifold with totally geodesic boundary has some connected finite covering space with more than one boundary component?

share|cite|improve this question
This follows from peripheral separability of incompressible surfaces in the boundary of a compact 3-manifold: – Ian Agol Oct 2 '11 at 15:44
A slightly older reference which applies in your case is a result of Long: Also to clarify, these techniques only apply in the case of finite-volume manifolds with totally geodesic boundary: I'm not sure what is known in the case of infinitely generated groups. – Ian Agol Oct 3 '11 at 0:48
thanks, this is extremely what i am looking for! – strygwyr Oct 3 '11 at 5:12
Agol: I think your comment would make a good answer. – S. Carnahan Oct 4 '11 at 8:27

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Browse other questions tagged or ask your own question.