Position after 21 Rd6.
In order to maximize his position, White needs to:
(i) Exploit the d6 outpost and open d-file
(ii) Invade with a timely e5-e6.
This thrust also liberates b2 along diagonal a1-h8.
21 ... Be6 22 Rfd1 Rb8 23 Qd3 Bxc4 24 Qxc4 b5
25 Qd5 c4 26 e6 Rg8 27 Qxf5 Nb7 28 Rd7 Qc5+
29 Qxc5 Nxc5 30 Rxa7.
21 ... Be6 22 Rfd1 b6 23 Qc3 Bxc4 24 Qxc4 Re8
25 Qd3 Qf8 26 Qd5 Rc8 27 e6 c4 28 bxc4 Rc5
29 Qd4 Nc6 30 Qc3 Ne7 31 Rd8 Rc8 32 Rxc8 Rxc8
33 Rd7 a5 34 Qf3 Kg8 35 Be5 Rxc4 36 Qb7 Re4.
Pawn vs Pawn.
When two opposing pawns are situated on
adjacent verticals and each on its Primary
Base Line, that side which has not the move
wins the adverse pawn.
Knight vs. Knight.
A Knight posted at R1 or R8, and having to move,
is lost if all the points on its periphery are
contained in an adverse Knight's octagon.
The Major Tactics Of Chess
FRANKLIN K. YOUNG