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'''[[Main Page|Home]] * [[Board Representation]] * [[Bitboards]] * [[Pawn Pattern and Properties]] * Backward Pawns'''
[[Hans Kmoch|Kmoch's]] definition of a [[Backward Pawn|backward pawn]] or Straggler: A half-free pawn on the second or third rank whose stop square lacks pawn protection but is controlled by a [[Sentry|sentry]]. The definition of a backward pawn seems a bit ambiguous. May an [[Isolated Pawns (Bitboards)|isolated pawn]] also be a backward one? Or an pawn on a [[Pawns and Files (Bitboards)#ClosedFiles|closed file]]? What about a backward [[Pawn Rams (Bitboards)|ram]] or [[Candidates (Bitboards)|faked candidates]] or even [[Pawn Levers (Bitboards)|levers]]?
<span id="Backward"></span>
=Backward=
We may use a more general definition of backwardness, to consider certain subsets independently. All pawns, which [[Pawn Spans#StopandDistantStop|stop]] is not member of own [[Attack Spans|front-attackspans]] but controlled by a sentry are '''backward''':
<pre>
U64 wBackward(U64 wpawns, U64 bpawns) {
U64 stops = wpawns << 8;
U64 wAttackSpans = wEastAttackFrontSpans(wpawns)
| wWestAttackFrontSpans(wpawns);
U64 bAttacks = bPawnEastAttacks(bpawns)
| bPawnWestAttacks(bpawns);
return (stops & bAttacks & ~wAttackSpans) >> 8;
}
</pre>
=Straggler=
Stragglers are the intersection of backward with [[Open Pawns (Bitboards)#OpenPawnsSetwise|open pawns]] and the second or third rank:
<pre>
U64 wStraggler(U64 wpawns, U64 bpawns) {
return wBackward (wpawns, bpawns)
& wOpenPawns(wpawns, bpawns)
& 0xffff00; // rank 2,3
}
</pre>
In the strict sense, we still need to exclude [[Pawn Levers (Bitboards)|levers]]. On the other hand, levers are subject of [[quiescence search]] anyway.
=Telestop Weakness=
As pointed out by [[Sam Hamilton]] <ref>[http://www.talkchess.com/forum/viewtopic.php?topic_view=threads&p=290991&t=29689 Re: Doubled and Backward Pawn Engine "Definitions"] by [[Sam Hamilton]], [[CCC]], September 13, 2009</ref> considering stop squares might be insufficient for pawns which may actually push, but have a permanent weakened [[Pawn Spans#StopandDistantStop|telestop]], f.i.:
<fentt border="double" style="font-size:24pt">8/5p2/6p1/p1p3P1/P1P5/7P/1P6/8</fentt>
8/5p2/6p1/p1p3P1/P1P5/7P/1P6/8 w - -
On the other hand, such a backward prospective pawn has a vital [[Tempo|tempo]], which is often decisive in certain [[Pawn Endgame|pawn endings]], so one should be careful to don't make the penalty too worse. Anyway, one may either apply the above [[Backward Pawns (Bitboards)#Backward|wBackward]] algorithm with so far movable pawns shifted one rank up, or alternatively determine a ''backward square area'', which is the black [[Attack Spans|attack span]] of all black attacks which are outside the white [[Attack Spans|front attack spans]]:
<pre>
white pawns black pawns
. . . . . . . . . . . . . . . .
. . . . . . . . . . . . . 1 . .
. . . . . . . . . . . . . . 1 .
. . . . . . 1 . 1 . 1 . . . . .
1 . 1 . . . . . . . . . . . . .
. . . . . . . 1 . . . . . . . .
. 1 . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . .
~white front & black attacks -> stop squares
attackspans dominated by black
. . . . 1 . . . . . . . . . . . . . . . . . . .
. . . . 1 . . . . . . . . . . . . . . . . . . .
. . . . 1 . . . . . . . 1 . 1 . . . . . 1 . . .
. . . . 1 1 . 1 . . . . . 1 . 1 . . . . . 1 . 1
. 1 . 1 1 1 . 1 & . 1 . 1 . . . . . 1 . 1 . . . .
. 1 . 1 1 1 1 1 . . . . . . . . . . . . . . . .
1 1 1 1 1 1 1 1 . . . . . . . . . . . . . . . .
1 1 1 1 1 1 1 1 . . . . . . . . . . . . . . . .
stop squares
dominated by black
filled down
-> white & white pawns -> backward pawns
backward area
. . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . .
. . . . 1 . . . . . . . . . . . . . . . . . . .
. . . . 1 1 . 1 . . . . . . 1 . . . . . . . . .
. 1 . 1 1 1 . 1 & 1 . 1 . . . . . . . . . . . . .
. 1 . 1 1 1 . 1 . . . . . . . 1 . . . . . . . 1
. 1 . 1 1 1 . 1 . 1 . . . . . . . 1 . . . . . .
. 1 . 1 1 1 . 1 . . . . . . . . . . . . . . . .
</pre>
=Dynamic Backwardness=
==A further Pass==
Another issue is that some pawns or their stop squares are statically member of their own [[Attack Spans|attack spans]], but those spans could not be realized, since their pawns are either backward or [[Pawn Rams (Bitboards)|rammed]] (or both). Those pawns (f.i. white pawn c4, and mutually black pawn a4 in the diagram) may determined in a second pass, only considering attack spans of movable pawns.
<fentt border="double" style="font-size:24pt">8/8/1p6/8/p1P1p3/3pP3/1P1P4/8</fentt>
8/8/1p6/8/p1P1p3/3pP3/1P1P4/8 w - -
==Stops with negative SEE==
A more sophisticated definition of backwardness was given by [[Vincent Diepeveen]] <ref>[https://www.stmintz.com/ccc/index.php?id=272903 Re: WHAT is the definition of a backward pawn?] by [[Vincent Diepeveen]], [[CCC]], December 24, 2002</ref>, even a member of a [[Duo Trio Quart (Bitboards)|pawn duo]] may be backward, if its stop square has a negative [[Static Exchange Evaluation|SEE]] score, also considering pieces. Here b7 is considered backward, no matter whether the other friendly pawn is on c7 or c6, since it's stop square b6 has a negative SEE in both cases.
<fentt border="double" style="font-size:24pt">8/1pp5/8/2P5/8/8/8/1R6</fentt>
8/1pp5/8/2P5/8/8/8/1R6 w - -
=See also=
* [[Backward Pawn]]
* [[Open Pawns (Bitboards)|Open Pawns]]
* [[Sentry]]
* [[Attack Spans]]
* [[Candidates (Bitboards)#Sneaker|Sneaker]] from [[Candidates (Bitboards)]]
* [[Hidden Passed Pawn]]
* [[Faker]]
* [[Hans Kmoch]]
=Publications=
* [[Hans Kmoch]] ('''1959, 1990'''). ''Pawn Power in Chess''. New York: Dover, 1990. Previous ed.: New York: McKay, 1959. ISBN 0-486-26486-6
=Forum Posts=
* [https://www.stmintz.com/ccc/index.php?id=272739 WHAT is the definition of a backward pawn?] by [[Bas Hamstra]], [[CCC]], December 23, 2002
* [http://www.talkchess.com/forum/viewtopic.php?t=20320 Backward Pawns] by [[Mark Lefler]], [[CCC]], March 24, 2008
* [http://www.talkchess.com/forum/viewtopic.php?t=29689 Doubled and Backward Pawn Engine "Definitions"] by [[Brian Richardson]], [[CCC]], September 07, 2009
* [http://www.talkchess.com/forum/viewtopic.php?t=52300 What is a backward pawn?] by [[Lyudmil Tsvetkov]], [[CCC]], May 12, 2014
=External Links=
* [https://en.wikipedia.org/wiki/Backward_pawn Backward pawn from Wikipedia]
=References=
<references />
'''[[Pawn Pattern and Properties|Up one Level]]'''
[[Category:Hans Kmoch]]
[[Hans Kmoch|Kmoch's]] definition of a [[Backward Pawn|backward pawn]] or Straggler: A half-free pawn on the second or third rank whose stop square lacks pawn protection but is controlled by a [[Sentry|sentry]]. The definition of a backward pawn seems a bit ambiguous. May an [[Isolated Pawns (Bitboards)|isolated pawn]] also be a backward one? Or an pawn on a [[Pawns and Files (Bitboards)#ClosedFiles|closed file]]? What about a backward [[Pawn Rams (Bitboards)|ram]] or [[Candidates (Bitboards)|faked candidates]] or even [[Pawn Levers (Bitboards)|levers]]?
<span id="Backward"></span>
=Backward=
We may use a more general definition of backwardness, to consider certain subsets independently. All pawns, which [[Pawn Spans#StopandDistantStop|stop]] is not member of own [[Attack Spans|front-attackspans]] but controlled by a sentry are '''backward''':
<pre>
U64 wBackward(U64 wpawns, U64 bpawns) {
U64 stops = wpawns << 8;
U64 wAttackSpans = wEastAttackFrontSpans(wpawns)
| wWestAttackFrontSpans(wpawns);
U64 bAttacks = bPawnEastAttacks(bpawns)
| bPawnWestAttacks(bpawns);
return (stops & bAttacks & ~wAttackSpans) >> 8;
}
</pre>
=Straggler=
Stragglers are the intersection of backward with [[Open Pawns (Bitboards)#OpenPawnsSetwise|open pawns]] and the second or third rank:
<pre>
U64 wStraggler(U64 wpawns, U64 bpawns) {
return wBackward (wpawns, bpawns)
& wOpenPawns(wpawns, bpawns)
& 0xffff00; // rank 2,3
}
</pre>
In the strict sense, we still need to exclude [[Pawn Levers (Bitboards)|levers]]. On the other hand, levers are subject of [[quiescence search]] anyway.
=Telestop Weakness=
As pointed out by [[Sam Hamilton]] <ref>[http://www.talkchess.com/forum/viewtopic.php?topic_view=threads&p=290991&t=29689 Re: Doubled and Backward Pawn Engine "Definitions"] by [[Sam Hamilton]], [[CCC]], September 13, 2009</ref> considering stop squares might be insufficient for pawns which may actually push, but have a permanent weakened [[Pawn Spans#StopandDistantStop|telestop]], f.i.:
<fentt border="double" style="font-size:24pt">8/5p2/6p1/p1p3P1/P1P5/7P/1P6/8</fentt>
8/5p2/6p1/p1p3P1/P1P5/7P/1P6/8 w - -
On the other hand, such a backward prospective pawn has a vital [[Tempo|tempo]], which is often decisive in certain [[Pawn Endgame|pawn endings]], so one should be careful to don't make the penalty too worse. Anyway, one may either apply the above [[Backward Pawns (Bitboards)#Backward|wBackward]] algorithm with so far movable pawns shifted one rank up, or alternatively determine a ''backward square area'', which is the black [[Attack Spans|attack span]] of all black attacks which are outside the white [[Attack Spans|front attack spans]]:
<pre>
white pawns black pawns
. . . . . . . . . . . . . . . .
. . . . . . . . . . . . . 1 . .
. . . . . . . . . . . . . . 1 .
. . . . . . 1 . 1 . 1 . . . . .
1 . 1 . . . . . . . . . . . . .
. . . . . . . 1 . . . . . . . .
. 1 . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . .
~white front & black attacks -> stop squares
attackspans dominated by black
. . . . 1 . . . . . . . . . . . . . . . . . . .
. . . . 1 . . . . . . . . . . . . . . . . . . .
. . . . 1 . . . . . . . 1 . 1 . . . . . 1 . . .
. . . . 1 1 . 1 . . . . . 1 . 1 . . . . . 1 . 1
. 1 . 1 1 1 . 1 & . 1 . 1 . . . . . 1 . 1 . . . .
. 1 . 1 1 1 1 1 . . . . . . . . . . . . . . . .
1 1 1 1 1 1 1 1 . . . . . . . . . . . . . . . .
1 1 1 1 1 1 1 1 . . . . . . . . . . . . . . . .
stop squares
dominated by black
filled down
-> white & white pawns -> backward pawns
backward area
. . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . .
. . . . 1 . . . . . . . . . . . . . . . . . . .
. . . . 1 1 . 1 . . . . . . 1 . . . . . . . . .
. 1 . 1 1 1 . 1 & 1 . 1 . . . . . . . . . . . . .
. 1 . 1 1 1 . 1 . . . . . . . 1 . . . . . . . 1
. 1 . 1 1 1 . 1 . 1 . . . . . . . 1 . . . . . .
. 1 . 1 1 1 . 1 . . . . . . . . . . . . . . . .
</pre>
=Dynamic Backwardness=
==A further Pass==
Another issue is that some pawns or their stop squares are statically member of their own [[Attack Spans|attack spans]], but those spans could not be realized, since their pawns are either backward or [[Pawn Rams (Bitboards)|rammed]] (or both). Those pawns (f.i. white pawn c4, and mutually black pawn a4 in the diagram) may determined in a second pass, only considering attack spans of movable pawns.
<fentt border="double" style="font-size:24pt">8/8/1p6/8/p1P1p3/3pP3/1P1P4/8</fentt>
8/8/1p6/8/p1P1p3/3pP3/1P1P4/8 w - -
==Stops with negative SEE==
A more sophisticated definition of backwardness was given by [[Vincent Diepeveen]] <ref>[https://www.stmintz.com/ccc/index.php?id=272903 Re: WHAT is the definition of a backward pawn?] by [[Vincent Diepeveen]], [[CCC]], December 24, 2002</ref>, even a member of a [[Duo Trio Quart (Bitboards)|pawn duo]] may be backward, if its stop square has a negative [[Static Exchange Evaluation|SEE]] score, also considering pieces. Here b7 is considered backward, no matter whether the other friendly pawn is on c7 or c6, since it's stop square b6 has a negative SEE in both cases.
<fentt border="double" style="font-size:24pt">8/1pp5/8/2P5/8/8/8/1R6</fentt>
8/1pp5/8/2P5/8/8/8/1R6 w - -
=See also=
* [[Backward Pawn]]
* [[Open Pawns (Bitboards)|Open Pawns]]
* [[Sentry]]
* [[Attack Spans]]
* [[Candidates (Bitboards)#Sneaker|Sneaker]] from [[Candidates (Bitboards)]]
* [[Hidden Passed Pawn]]
* [[Faker]]
* [[Hans Kmoch]]
=Publications=
* [[Hans Kmoch]] ('''1959, 1990'''). ''Pawn Power in Chess''. New York: Dover, 1990. Previous ed.: New York: McKay, 1959. ISBN 0-486-26486-6
=Forum Posts=
* [https://www.stmintz.com/ccc/index.php?id=272739 WHAT is the definition of a backward pawn?] by [[Bas Hamstra]], [[CCC]], December 23, 2002
* [http://www.talkchess.com/forum/viewtopic.php?t=20320 Backward Pawns] by [[Mark Lefler]], [[CCC]], March 24, 2008
* [http://www.talkchess.com/forum/viewtopic.php?t=29689 Doubled and Backward Pawn Engine "Definitions"] by [[Brian Richardson]], [[CCC]], September 07, 2009
* [http://www.talkchess.com/forum/viewtopic.php?t=52300 What is a backward pawn?] by [[Lyudmil Tsvetkov]], [[CCC]], May 12, 2014
=External Links=
* [https://en.wikipedia.org/wiki/Backward_pawn Backward pawn from Wikipedia]
=References=
<references />
'''[[Pawn Pattern and Properties|Up one Level]]'''
[[Category:Hans Kmoch]]
