Convergence of Baumslag-Solitar groups
  We study convergent sequences of Baumslag-Solitar groups in the space of marked groups. We prove that BS(m,n) --> F_2 for |m|,|n| --> \infty and BS(1,n) --> Z \wr Z for |n| --> \infty. For m fixed, |m|>1, we show that the sequence (BS(m,n))_n is not convergent and characterize many convergent subsequences. Moreover if X_m is the set of BS(m,n)'s for n relatively prime to m and |n|>1, then the map BS(m,n) \mapsto n extends continuously on the closure of X_m to a surjection onto invertible m-adic integers. 
Yves Stalder (Universite de Neuchatel)