15. The following recursively defined function will tile a 2" x 2" checkerboard, with one square deleted, with the required amount of L-shaped tiles three squares large. procedure tile (C: 2" x 2" checkerboard with one square deleted) if n = 1 then lay down a single tile in the only possible way else begin Cut the board up into four 2n-1 x 2n-1 sub-boards tile (the sub-board with the missing piece) for i 1 to 3 = begin B:= the next sub-board not already tiled B: B with the central corner removed tile (B) end tile (the three squares in the middle that are still untiled) end Show the step-by-step solution for: procedure tile (C3).