Easy as First or Second ABCD (573)

Place letters A, B, C, D in the cells, so that each letter appears exactly once in each row and column. Each cell must have at most one letter, but can be empty. Clues of the form ‘X1’ indicate the first letter and clues of the form ‘X2’ indicate the second letter in the respective row or column, seen from that direction.

Reference: WPF (1)