The Yellow Cake
  We consider the following property:   (*) For every function f from R^2 to R there are functions g_n,h_n from R to R (for n<omega) such that for all real numbers x and y, f(x,y) = sum_{n<omega} g_n(x)h_n(y).   We show that, despite some expectation suggested by [Sh:675], (*) does not imply MA(sigma-centered). Next, we introduce cardinal characteristics of the continuum responsible for the failure of (*). 
Andrzej Roslanowski and Saharon Shelah