Before revision: Jeandel and Rao proved that 11 is the size of the smallest set of Wang tiles, i.e., unit squares with colored edges, that admit valid  (contiguous edges of adjacent tiles have the same color) tilings of the plane  none of them being invariant under a nontrivial translation.
After revision: Jeandel and Rao proved that 11 is the size of the smallest set of Wang tiles, i.e., unit squares with colored edges, that admit valid (contiguous edges of adjacent tiles have the same color) tilings of the plane , none of them being invariant under a nontrivial translation.