Extendibility of bilinear forms on Banach sequence spaces
  We study Hahn-Banach extensions of multilinear forms defined on Banach sequence spaces. We characterize $c_0$ in terms of extension of bilinear forms, and describe the Banach sequence spaces in which every bilinear form admits extensions to any superspace. 
Daniel Carando and Pablo Sevilla-Peris
math.FA