[Poincar\'e duality groups of dimension 2 are surface groups.][1] 



  [1]: http://books.google.com/books?id=zaLQFGI-1AoC&lpg=PA51&dq=poincare%2520duality%2520groups%2520of%2520dimension%2520two&pg=PA35#v=onepage&q&f=false