  We consider the problem of computing (irregular) conformal blocks in 2d CFTs
whose chiral symmetry algebra is the N=2 superconformal algebra. Our
construction uses two ingredients: (i) the relation between the representation
theories of the N=2 superconformal algebra and the affine sl(2) algebra,
extended to the level of the conformal blocks, and (ii) the relation between
affine sl(2) conformal blocks and instanton partition functions in the 4d N=2
SU(2) gauge theory with a surface defect. By combining these two facts we
derive combinatorial expressions for the N=2 superconformal blocks in the
Gaiotto limit.
