Approximate and global differentiability of functions over   non-archimedean fields
  The article is devoted to approximate, global and along curves differentiability of functions over non-archimedean infinite fields with non-trivial valuations. Fields with zero and non-zero characteristics are considered. Spaces of differentiable functions are defined with the help of partial difference quotients. Approximate differentiability is studied relative to real-valued measures. Theorems about relations between these three types of differentiability are proved. Associated problem on extensions of such functions is investigated. 
S.V. Ludkovsky