Problem bank

Problem 137 of 333HardBrainteaserP137

Flipping 3×3 and 4×4 blocks in an 8×8 grid

  1. An 8×88 \times 8 grid has each cell containing 0 or 1. You may repeatedly pick any 3×33 \times 3 or 4×44 \times 4 sub-block and flip every bit in it. Can every initial configuration be reduced to the all-zero grid?