Dehn functions and the space of marked groups
  In the space of marked group, we suppose that a sequence $(G_i, X_i)$ converges to $(G,X)$, where $G$ is finitely presented. We obtain an inequality which connects Dehn functions of $G_i$s and $G$. As a result, we show that if a sequence $(K, X_i)$ converges to a hyperbolic marked group, then $K$ is already hyperbolic. 
M. Shahryari
math.GR