...16.K to B sq.

Black cannot play 16. Kt to K 3, because he would thereby leave his K P en prise; he cannot castle, because then his K R P would be en prise; and if he were to return with the Kt to B 3, he would have lost a move. Therefore he has nothing better than to move his King into safety to B sq., and then to Kt 2.

17.Q to Q 2 (?)17.K to Kt 2
18.P to K R 3...

To prevent Black from playing 18. ... B takes B; Q takes B, Kt to Kt 5, attacking the Queen.

...18.Kt to B 3
19.Kt to R 419.Q R to Q sq.

Occupying the "open file" and defending the Bishop, so as to free his K Kt, which was before fixed, as it had to defend the Bishop.

20.B takes B20.R P takes B

It is, in the majority of these cases, better to take with the R P, because it gives an additional "open file" for the entry of the Rook.