1.f6
[ 1.a4??
loses to 1...Kg3
( or 1...bxa3
2.bxa3
Kg3
and mate in six) 2.a5
h5
3.a6
h4
4.a7
h3
5.a8Q
h2#
; 1.Kxg2
to avoid being mated 1...Kg5
2.a4
bxa3
3.bxa3
Kf6
and Black can stop the a-pawn. 4.a4
Ke7
5.a5
Kd8
6.a6
Kc8
7.a7
Kb7
]
1...gxf6
2.Kxg2
White has blocked the defensive route for the black king to d8-c8-b7, and also prevented the mate with the h-pawn.
2...Kg4
3.a4
bxa3
4.bxa3
Kf5
5.a4
Ke5
Now comes the second brilliant idea: to sacrifice the remaining white pawns to stop the black king, which is still in the promotion square of the a-pawn.
6.d6
cxd6
[ 6...c6
7.a5
]
7.c6
dxc6
Now the black king cannot reach the queening square of the a-pawn in time, since it is blocked by the two black pawns on c6 and d6!
8.a5
1-0