Where is there a mate in four (pawn moves)? From Fine's BCE:



I can only see the pawn getting to a2 after 1.d6+ Kd8 2.e6 a4 3.Kf6 a3 4.e7+ Ke8 5.Ke6 a2 6.d7#. That's three pawn moves, not four.

What is the more resistant defence I missed?
1.d6+ Ke8

2.e6 a4 (pawn move 1)

3.Kf6 a3 (pawn move 2) [Note: 3.e7 Kf7!]

4.e7 a2 (pawn move 3)

5.Ke6 a1=Q (pawn move 4)

6.d7 mate