FIDE Surveys – Iossif Dorfman

1

Iossif Dorfman:

Middle game with two Bishops
and a Knight against two
Knights and a Bishop

Middle game positions with a pair of
bishops and a knight against two knights and
a bishop can be seen very frequently in
practical games. I would like to share with
you my understanding of this problem.
Analyzing positions with this type of
materiel corellation allows us to draw the
following conclusions:
The side who has 2 knights and a bishop
(2N +B) must:
(1) exchange the pair of knights,
(2) also the bishops of the same color,
(3) create a conflict on the squares of his
bishop.
In certain positions it’s possible to trade the
bishop against the knight. On the one hand
it’s the struggle of colors, and on the other
hand the purpose is to obtain the best
tandem of queen and knight against queen
and bishop. What’s important to understand:
in reality two knights and a bishop attack
together the squares of the bishop’s color (3
pieces against 2) and resist on the squares of
the opposite color (2 against 2).
The opposite side with two bishops and
knight (2B+N) must:
(1) exchange the queens,
(2) create a conflict on the squares of his
“extra” bishop.
Also, in certain positions it’s possible to
give a bishop against a knight.
This article highlights two recent games
where we can observe the theoretical
dispute.

Vachier-Lagrave : Caruana
Karlsruhe/Baden Baden 2018

1.c4 e5 2.Sc3 Sf6 3.Sf3 Sc6 4.g3 Lb4 5.Lg2
0–0 6.0–0 e4 7.Sg5 Lc3
Trading bishop for knight seems correct
here.
8.bc3 Te8 9.Dc2?

XIIIIIIIIY
9r+lwqr+k+0
9zppzpp+pzpp0
9-+n+-sn-+0
9+-+-+-sN-0
9-+P+p+-+0
9+-zP-+-zP-0
9P+QzPPzPLzP0
9tR-vL-+RmK-0
xiiiiiiiiy

The destiny of the variation depends of 9.f3
e3. This move was introduced in practice by
Karpov's stuff. Logically, black should
develop the conflict on the light coloured
squares by 9...ef3 10.Sf3 d5, but after 11.d4
h6 12.Dc2, invented by Kasparov, Black
failed to demonstrate enough counterplay
(12.cd5 Dd5 13.e3
a) 13.Se5 De6 14.Sd3 De2 15.De2 (15.Lh6
Dd1 16.Tad1 Lg4 17.Td2 Le2 18.Tf6 gf6
19.Sc5 Lc4 20.Kf2 Sa5 21.Se4 Te6 22.d5
Ta6 23.Sc5 Tb6 24.Le3 Lb5 25.Sb3 Sc4
26.Lb6 Sd2 (Black maintains a favorable
position after 26...ab6 27.Tc2 Sd6) 27.Lc7
Te8 28.a4 Te2 29.Kg1 Sb3 30.ab5 Tc2
31.d6 Sc5 32.Lh3 Tc3 33.b6 a5 34.d7 Sd7
35.Ld7 Tc4 36.Lc8 a4 37.Lb7 a3 38.Ld5 a2
39.Lc4 a1D 40.Lf1 (Probably even without
b-pawn White builds a fortress.) 40...Db1
41.Kf2 Db2 42.Le2 Dd4 43.Kg2 f5 44.Lf3
Dd2 45.Kf1 Kf8 46.Le2 Dc1 47.Kg2 De1
48.Lf3 Da5 49.h4 ½, Wolter : Knogler,
www.remoteschach.de 2017) 15...Te2
16.Lh6 Se4 17.d5 Se7 18.Lf3 Sc3 19.Le2

FIDE Surveys – Iossif Dorfman

2

Se2 20.Kf2 Sc3 21.d6 Sed5 22.Lc1 cd6
23.Sf4 Se4 24.Kg1 Sb4 25.Lb2 Ld7 26.Tfe1
Lc6 27.Te2 Sa6 28.Td1 f6 29.Te3 Kf7
30.Sd5 ½, Buettner : Knogler,
www.remoteschach.de 2017;
b) 13.e4 De4 14.Se5 Dh7 15.Lf4 Se5 16.de5
Sd7 17.e6 Te6 18.Lc7 Dg6 19.Dd4 Sf6
20.Le5 Sg4 21.Lf4 Te8 22.h3 ½, Daanen :
Ziegler, FICGS 2017.
13...Lf5

XIIIIIIIIY
9r+-+r+k+0
9zppzp-+pzp-0
9-+n+-sn-zp0
9+-+q+l+-0
9-+-zP-+-+0
9+-zP-zPNzP-0
9P+-+-+LzP0
9tR-vLQ+RmK-0
xiiiiiiiiy

On the diagram is, perhaps, one of the most
striking illustrations of the theory studied
here. Black gained control over light-
coloured squares and is ready to exchange
the bishops.
14.Sd2 Dd7 15.Sb3 Se4 16.c4 b6 17.Tf4
(17.Sd2 Sd2 18.Ld2 Le4. Exchange of
knights and bishops.
In case of the useless 17.Lb2 Lh3 18.Lh3
Dh3 19.De2 Se7 20.Sd2 Sd2 21.Dd2 Sf5
22.Tae1 Sd6 Black is better due to the safe
king and the tandem of queen and knight.)
17...Tad8 18.Df1 Lg6 19.La3 Sa5
(19...Sg5 20.h4 Te3 21.hg5 hg5 22.Tf3 Tf3
23.Lf3 Sd4 24.Ld5 c6 25.Td1 cd5 26.Td4
Te8 27.Lb4 Da4 28.cd5 Da2 and Black is
out of danger.)
20.Lb4 Sb3 21.ab3 c5
(21...a5 22.La3 Sg5 23.h4 Te3 24.hg5 hg5
25.Tf3 Dd4 26.Te3 De3 27.Df2 Db3.)
22.Le4 Te4 23.Te4 Le4 24.Lc3 Lc2 25.b4
cb4 26.Lb4 a5 27.Lc3 Tc8 28.Tc1 Lb3 29.c5

De6 (29...a4 30.cb6 De6) 30.Df4 a4 31.e4
bc5 32.d5 Dd7 33.h4 f6 34.g4 Te8 35.Te1
Lc2 36.g5 hg5 37.hg5 fg5 38.Dg5 Te4
39.Te4 Le4 40.d6 a3 41.Dc5 Dg4 42.Kf2
Df3 43.Ke1 Dg3 44.Kd2 Dd3 45.Ke1 a2
46.Dd4 Dg3 47.Kd2 Dg2 48.Ke3 Df3
49.Kd2 Dg2 50.Ke3 Lf5 51.d7 Dg3 52.Ke2
Lg4 53.Kf1 Lh3 54.Ke2 Dg2 55.Ke1 Dg3
56.Ke2 Dg2 ½, Aronian : Adams, Baden-
Baden 2015)

12...dc4 13.Lf4

XIIIIIIIIY
9r+lwqr+k+0
9zppzp-+pzp-0
9-+n+-sn-zp0
9+-+-+-+-0
9-+pzP-vL-+0
9+-zP-+NzP-0
9P+Q+P+LzP0
9tR-+-+RmK-0
xiiiiiiiiy

13...Sd5
In case of very logical 13...Se4 14.Tad1 Lf5
I saw a very instructive win by Caruana:
15.Se5 Sd6 16.e4 Lh7 17.De2 Se7. Black is
already in difficult situation and by subtle
sacrifice of piece 18.Lh6 White
demonstrates the shortest way to destroy the
opponent's defense: 18...gh6 19.Dh5 Sef5
20.ef5 Dg5 21.Dg5 hg5 22.f6 Se4 23.Tfe1
Sc3 24.Tc1 Sb5 25.Lb7 Tad8 26.Lc6 Sd4
27.Le8 Te8 28.Kf2 Sc2 29.Ted1 Le4 30.Sc4
Te6 31.Td8 Kh7 32.Kg1 Tf6 33.Tf1 1:0,
Caruana : Anand, Moscow 2016.
14.e4 Sf4 15.gf4
Obviously, this position requires special
analysis.

FIDE Surveys – Iossif Dorfman

3

XIIIIIIIIY
9r+lwqr+k+0
9zppzp-+pzp-0
9-+n+-+-zp0
9+-+-+-+-0
9-+pzPPzP-+0
9+-zP-+N+-0
9P+Q+-+LzP0
9tR-+-+RmK-0
xiiiiiiiiy

15...Tb8 (At the moment, the struggle ends
with equality after 16.Df2 a6 17.Tae1 b5
18.f5 b4 19.e5 bc3 20.f6 Dd7 21.d5 Dd5
22.Sh4 Db5 23.Dg3 Dc5 (½, Zielinski :
Knogler, www.remoteschach.de 2017.)
24.Kh1 g5 25.Sf3 g4 26.Df4 Df8 27.Sh4
27...Se5 (Unsufficient is 27...Te5 28.Lc6
Te1 29.Te1 c2 30.Sf5 Lf5 31.Df5 Tb1
32.Tb1 cb1L 33.Db1 Dd8 34.De4.) 28.Te5
Te5 29.De5 c2 30.Dc3 Tb1 31.Dc2 Tf1
32.Lf1 Dd6 33.Dc3 Lb7 34.Sg2 Le4 35.Dc4
Df6)
10.d3
Apparently necessary. 10.de3 allows Black
to increase the pressure and exploit the
weaknesses of the queenside by statical
10...De7 11.e4
a) 11.Sh3 Dc5 12.Sf4 Dc4 13.e4 d6 14.Dd3
Le6 (14...Se5 15.Dc4 Sc4 16.g4 Tb8 17.Td1
b6 18.g5 Sd7 19.Sd5 Tb7 20.f4 Sf8 21.Td4
Sa5 22.f5 Ld7 23.Tb1 c5 24.Td3 La4 25.Lf4
Lc2 26.Tb2 Ld3 27.ed3 Td8 28.h4 Sc6
29.h5 Se7 30.Se3 Tbd7 31.Sg4 Sc6 32.h6
Se5 33.Le5 de5 34.hg7 Kg7 35.Lf1 Td6
36.Se5 f6 37.Sg4 fg5 38.Th2 Te8 39.e5 Td5
40.f6 Kh8 41.Sh6 Tde5 42.Sf7 Kg8 43.Sh6,
½, Kasparov : Sadvakasov, Astana 2001)
15.Le3 ½, Khalifman : Grischuk, Kallithea
2002;
b) 11.f4 (White creates new wholes in the
hope of exploiting activity of his pieces.)

11...h6 12.Sf3 b6 13.Sd4 Lb7 14.Lf3 Se4
15.Dd3 Sc5 16.Dc2 Sa5 17.Ld5 a6 18.Td1
Se4 19.Dd3 Ld5 20.cd5 b5

XIIIIIIIIY
9r+-+r+k+0
9+-zppwqpzp-0
9p+-+-+-zp0
9snp+P+-+-0
9-+-sNnzP-+0
9+-zPQzP-zP-0
9P+-+P+-zP0
9tR-vLR+-mK-0
xiiiiiiiiy

Instructive play on blockade. 21.Sf3 (21.a4
is just met by 21...Sc5 (or 21...ba4) )
21...Sc4 22.Se5 Sc5 23.Dd4 Se5 24.fe5 Sa4
25.d6 cd6 26.Dd6 Dg5, with the decisive
advantage for Black, 0:1, Mrugala :
Branding, ICCF email 2002.
11...Dc5 12.Kh1 h6 13.Sh3 Dc4 14.Sf4 d6
15.Dd2 b6 16.Td1 La6 (White has no
counterplay, and Black can calmly wait for
exchange of knights on "d5".) 17.Tb1 Tad8
18.Tb2 Da4 19.De1 Lc4 20.Sd5 Sd5 21.ed5
Se5 22.Dd2 Da6. White is completely
overplayed, 0:1, Conquest : David,
Liverpool 2008)
10...d5 11.Da4 h6 12.cd5 Sd5 13.Se4 f5
14.Sc5 f4
(Black is forced to play on the dark-coloured
squares, which is against my theory.)
15.Lb2 Tb8 16.Tab1 De7 17.c4 Sb6 18.Da3
Lf5 19.gf4 Dh4 20.Dc3 Te7 21.De1 Df4
22.Dg3 g5 23.Se4 Sd7 24.De1 Kh7 25.Dc3
Lg6 26.Lc1 g4 27.d4.
Finally, White wins e-pawn and the game,
1:0, Romanov : Tomashevsky, Sochi 2018.
9...d5 10.cd5 Dd5 11.d3 Lf5 12.Lf4 h6
13.Se4
The forced exchange of knights favors the
strategy of Black.
13...Se4 14.Db2 b6 15.Tfd1 Dc5

FIDE Surveys – Iossif Dorfman

4

16.de4 Le4

XIIIIIIIIY
9r+-+r+k+0
9zp-zp-+pzp-0
9-zpn+-+-zp0
9+-wq-+-+-0
9-+-+lvL-+0
9+-zP-+-zP-0
9PwQ-+PzPLzP0
9tR-+R+-mK-0
xiiiiiiiiy

Honestly, with all my respect to Maxime, I
don't understand what was unexpected for
him. After a series of very obvious moves,
Black is one step away from a profitable
tandem, and the white king's weakness does
not improve the situation.
17.Lf1 Te7 18.a4 Tae8 19.Tac1 g5 20.Ld2
Df5!
An excellent move to increase the pressure.
The threat to bring the knight on f3 via e5
provoke new weaknesses and, finally, so
desirable exchange of bishops.
21.f3 Dc5 22.Kh1 Ld5 23.Le1 Lc4 24.e4
In case of 24.Td2 Se5 white fails to parry
the tactical blows 25.Lg2 (25.Dc2 Sf3)
25...Sd3.
24...Lf1 25.Lf2 Dc4 26.Tf1 Da4
Now Black wins a pawn in much better
position.
27.c4 Se5 28.Ld4 g4 29.fg4 Dd7 30.Dc3 c5
31.Le5 Te5 32.Df3 Te4 33.Tcd1 De6 34.g5
hg5 35.Td5 g4 36.Dc3 Te5 0:1.

Houdini 6.03 : Stockfish 260318
TCEC Season 11 - Superfinal 2018

1.d4 Sf6 2.c4 e6 3.Sc3 Lb4 4.Dc2 c5 5.dc5
0–0 6.a3 Lc5 7.Sf3 b6
Played with the intention to get the
hedgehog.
8.Lf4

The most ambitious move is 8.e4, but the
weakening of the squares "d4" and "f2" is
felt in the following options.
8...Sg4

a)

After 8...Lb7 9.b4! White received an
important strategic advantage (9.Ld3 h6
(9...Sg4 10.0–0 Sc6 11.h3 Sge5 12.Se5 Se5
13.Td1 Dh4 14.b4 Ld4 15.Ta2 Sd3 16.Dd3
Lc3 17.Dc3 De4 18.f3 Dc6, ½, Brunner :
Nikolov, Monthey 2013) 10.0–0 Sc6 11.Lf4
Sh5 12.Ld2 Df6 13.Se2 a5 14.Lc3 De7
15.Tad1 d6 16.Kh1 Sf6 17.Sc1 a4 18.De2
Sg4 19.Lc2 Sge5 20.Sd3 Sf3 21.Df3 Sd4
22.Dg3 e5, 0:1, Morozevich : Ponkratov,
Sochi 2016.) 9...Le7 10.e5 Se8 11.Ld3 f5
12.ef6 Sf6 13.Se4 Se4 14.Le4 Le4 15.De4
Sc6 16.0–0 Dc7 17.Td1 Tac8 18.Le3

XIIIIIIIIY
9-+r+-trk+0
9zp-wqpvl-zpp0
9-zpn+p+-+0
9+-+-+-+-0
9-zPP+Q+-+0
9zP-+-vLN+-0
9-+-+-zPPzP0
9tR-+R+-mK-0
xiiiiiiiiy

½, Girya : Ju Wenjun, Chengdu 2016.
b) Here Black can try to get rid of the
backward pawn by 8...d5 but after 9.Lg5
White controls the situation in both, 9...d4
(and 9...de4 10.Lf6 Df6 11.De4 Ld7 12.Ld3
g6 13.Da8 Lc6 14.Da7 Lf3 15.0–0 Dg5
16.g3 Dg4 17.Tfe1 Sc6 18.Dc7 Sd4 19.Df4
Df4 20.gf4 Td8 21.b4 Ld6 22.Sb5 Sb3
23.Le4.) 10.Td1 e5 11.Lf6 gf6 12.Sd5 Kh8
13.b4 Le7 14.Ld3 a5 15.Sh4 Sc6 16.Dd2
Tg8 (16...ab4 17.ab4 Ta4 18.Tb1) 17.0–0
Lh3 18.Kh1 Le6 19.Sf5 Lf8 20.Tb1.
9.Lg5 (9.h3 is the most consistent
continuation, but Black succeeds in dynamic
counterplay by 9...Sf2 10.Th2 d5 11.g3 de4

FIDE Surveys – Iossif Dorfman

5

12.Se4 Se4 13.De4 Dc7 14.Lf4 Lb7 15.Lc7
Le4, 0:1, Pitkaenen : Gerbich, ICCF email
2011.) 9...f6 10.Lh4 Sc6 (Pressure on weak
squares "d4" and "b3" allows to look into
the future without fear in the very similar
variation.) 11.Td1 (Note that 11.Le2 is
always met by 11...a5 12.Td1 De7 13.h3
Sge5 14.Se5 Se5 15.0–0 La6 16.Sb5 Tac8
17.Db1 Sc6 18.Lg3 e5 19.Sc3 Sd4 20.Ld3
De6 21.Sd5 a4 (21...Sb3 22.a4 Ld4 23.Kh1
d6 24.f4 De8 25.Dc2 Sc5 26.b3 Lb7 27.f5
Ld5 28.ed5 Dh5 29.Le4 Dg5 30.Tf3 Kf7
31.Te1 Dh5 32.Tef1 Dg5 33.Kh2 Dh6.)
22.Kh1 Sb3 23.f4 d6 24.Le1 Ld4.) 11...a5
12.Le2 De7 13.h3 Sge5 14.Se5 Se5 15.Lg3
Sc6 16.0–0 Sd4 17.Dd2 Lb7 18.Ld3 e5.
8...Lb7 9.Td1 Sc6 10.b4 Sh5 11.Lc1
A cavalry attack is untenable: 11.Sg5 g6
12.Lc1 Le7 13.Sf3 Tc8 14.e3 a5 15.b5 Sb8,
0:1, De Carlos Arregui : Borisovs, ICCF
email 2008.
11...Le7 12.e4 Dc7
An interesting idea is to give a pawn to
weaken the opponent's queenside by break
a7–a5.
13.Le2
Here I selected few examples of instructive
play from correspondent chess.
13.Sb5 Db8 14.Td7 Sf6 15.Td1 a5 (15...a6
16.Sc3 a5 17.b5 Se5 18.Se5 De5 19.f4 Dc5
20.Ld3 Sg4 21.Sa4 Dh5 22.De2 Tad8 23.g3
f5 24.h3 Dh6 25.Le3 Se3 26.De3 e5 27.Db6
Db6 28.Sb6 ef4 29.Sd5, ½, Wolkowski :
Schuster, www.remoteschach.de 2005.)
16.ba5 Ta5 17.Ld3 (17.Ld2 Ta8 18.Ld3 Se5
19.Se5 De5 20.Lc3 Df4 21.f3 Lc5 22.Lb4
Sd7 23.Dd2 Dh4 24.g3 De7 25.Lc5 Dc5
26.Le2 Lc6 27.Dd4 g6 28.Kf2 Lb5 29.Dc5
Sc5 30.cb5 Ta3, ½, Sergiev : Rawlings,
ICCF email 2011.) 17...Sa7 18.Sc3 Tc8
19.0–0 b5 20.Sd2 bc4 21.Sc4 Tac5 22.Sa4
Tc4 23.Lc4 La6 24.Sb2 Lc4 25.Sc4 Db5
26.a4 Dc4 27.Dc4 Tc4 28.Le3 Ta4 29.Ta1
Ta1 30.Ta1 Sc6 31.Ta8 Lf8 32.Lc5 Sd7
33.Ld6 f6 34.Tc8 Sa5, ½, Pitkaenen :
Rawlings, ICCF email 2010.

13...Tad8 14.g3 Sf6 15.0–0 d6 16.h3 Tc8
17.Le3 Tfd8 18.Tfe1 Se8 19.Ld3 Db8
20.Tc1 Sf6 21.Lf1 h6 22.De2 Sd7 23.Sd2
Lf6 24.f4 Se7
This preparatory move is essential. Black
has created a rather flexible defensive line.
25.Dd3 a6
Perhaps an exceptional game in hedgehog
where Black played a6 on the move 25!
26.Lg2 Lc6 27.De2 b5 28.cb5 ab5 29.Lf2

XIIIIIIIIY
9-wqrtr-+k+0
9+-+nsnpzp-0
9-+lzppvl-zp0
9+p+-+-+-0
9-zP-+PzP-+0
9zP-sN-+-zPP0
9-+-sNQvLL+0
9+-tR-tR-mK-0
xiiiiiiiiy

It seems to me that White has taken an
unjustified risk and now Black is begining
active action, moving on to the material
2N+B against 2B+N.
29...Lc3 30.Tc3 d5
White has a choice between two scenarios:
31.Tec1?
Probably with a more rational 31.e5! still it
was possible to maintain balance 31...d4
32.Ld4 Sf5 33.Lf2 Lg2 34.Tc8 Tc8 35.Kg2
Tc3 36.Sb1 (36.Ta1 Db7 37.De4 Da6
38.De2 Dc6) 36...Tb3 37.Kh2 Db7 38.Tc1
Sb6 39.Sc3 Sc4 40.g4 Se7 41.Sb5 Sa3
42.Sa3 Ta3 43.b5 Sg6 44.Tc4 Ta1 45.Dd3
Ta2 46.Kg1 Ta1.
31...de4 32.Se4 Sb6 33.Lf3 Sc4 34.Lc5 Sd5
35.Td3 Da8 36.Tcd1 Te8 37.Kh2 Db8
38.Te1

FIDE Surveys – Iossif Dorfman

6

XIIIIIIIIY
9-wqr+r+k+0
9+-+-+pzp-0
9-+l+p+-zp0
9+pvLn+-+-0
9-zPn+NzP-+0
9zP-+R+LzPP0
9-+-+Q+-mK0
9+-+-tR-+-0
xiiiiiiiiy

38...f5
Black dominate white squares and now is
looking for the exchanges of light-coloured
bishops and knights.
39.Sd2
In case of 39.Sf2 Black play for a direct
attack by 39...e5 40.Ld5 Ld5 41.Td5 ef4.
39...Sd2 40.Dd2

XIIIIIIIIY
9-wqr+r+k+0
9+-+-+-zp-0
9-+l+p+-zp0
9+pvLn+p+-0
9-zP-+-zP-+0
9zP-+R+LzPP0
9-+-wQ-+-mK0
9+-+-tR-+-0
xiiiiiiiiy

40...Sf6 41.Ld1 Le4 42.Td4 Kh7 43.De3
La8 44.Lc2 Dc7 45.De2 Le4 46.Ld3 Ld3
47.Dd3 Se4
The wildest dreams have come true and the
tandem queen and the knight does not leave
hopes for salvation.
48.Db5 Ted8 49.Tde4
Best practical chance. The game enters the
stage of realization of the advantage and the
computer plays perfectly.

49...fe4 50.De2 Dc6 51.De4 De4 52.Te4
Td2 53.Kg1 Ta2 54.Te6 Td8 55.Td6 Te8
56.Td1 Tee2 57.b5 Tec2 58.Ld6 Tg2
59.Kh1 Th2 60.Kg1 Tag2 61.Kf1 Tf2
62.Kg1 Thg2 63.Kh1 Th2 64.Kg1 Tfg2
65.Kf1 Tb2 66.Lc5 Tb5 67.Lb4 Th1
68.Ke2 Th3 69.Kf3 Th2 70.Td3 h5 71.Td4
Tb2 72.Td3 Tb6 73.Tc3 Tb1 74.Ke3 Tf6
75.Td3 Te6 76.Kf2 Tc6 77.Ke2 Tc2 78.Kf3
Tf1 79.Ke4 Tc6 80.Kd5 Ta6 81.Kc4 Tg1
81...Kg6 82.Kb5 Ta8.
82.Lc5 Tc1 83.Kb5 Ta8 84.Lb4 Tb8
85.Ka5 Tb1 86.Ka6 g6 87.Ka7 Te8
88.Kb7 Kg7 89.Kc6 Kf6 90.Kc7 Tc1
91.Kd7 Kf7 92.Tf3 Td1 93.Kc7 Ted8 94.f5
g5 95.Tf2 T1d3 96.a4 T8d4 97.Tb2 Tc4
98.Kb6 Td8 99.Kb7 Tdd4 100.Le1
I did not choose this game by chance, as the
play of the program with a rating of 3500 in
accordance with the postulates of my theory
is a certain confirmation of its viability 0:1.