Rectangular tileability and complementary tileability are undecidable
  Does a given a set of polyominoes tile some rectangle? We show that this problem is undecidable. In a different direction, we also consider tiling a cofinite subset of the plane. The tileability is undecidable for many variants of this problem. However, we present an algorithm for testing whether the complement of a finite region is tileable by a set of rectangles. 
Jed Yang
math.CO cs.CC cs.CG