The solution is a 4x4 grid of letters where each row and column match the corresponding regexes. So the 4 letters descending from the column marked (LN|K|D)* s

The solution is a 4x4 grid of letters where each row and column match the corresponding regexes. So the 4 letters descending from the column marked (LN|K|D)* should match the regex ^.(LN|K|D)*$ entirely. Hope that helps.