Pawn+Spans

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Span- and Fill-Pattern of pawns are used as a base for a lot of other pawn structure related stuff, to determine passers, candidates, isolanis etc. set-wise. Every pawn has a **frontspan** with stop - and **telestop** squares, a **rearspan** and a **lee**- and **luff**-side, while rook-pawns miss the lee-side. code white pawn d5: . . . f. . . . . . . r. . . .   movement . . . o. . . .     ^ l e e P l u f f      | . . . r. . . . . . . e. . . . . . . a. . . . . . . r. . . . code

A span of each individual pawn reflects either its distance to promotion (frontspan), or distance to its back rank (rearspan).

 =Front- and Rearspans= Front- and rearspans are the front- and rearfills shifted one step further in the fill-direction: code white frontspans   black rearspans 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  |  . . . . . . . . . . . . . . . .     . . . . . . . . . . . . . . . .     . . . . . . . .               north white pawns        black pawns . . . . . . . .    . . . . . . . . . . . . . . . .     . 1 . . . 1 1 . . . . . . . . .     1 . 1 . . . . 1 . . . . . . . .     . . . 1 . . . . 1 . . . . 1 . .     . . . . . . . . . . 1 . . . . .     . . . . . . . . . 1 1 . . . 1 1     . . . . . . . . . . . . . . . .     . . . . . . . .               south white rearspans    black frontspans . . . . . . . . |  . . . . . . . . . . . . . . . .  v. . . . . . . . . . . . . . . .    . 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 1 . 1 1 1 code

code format="cpp" U64 wFrontSpans(U64 wpawns) {return nortOne (nortFill(wpawns));} U64 bRearSpans (U64 bpawns) {return nortOne (nortFill(bpawns));} U64 bFrontSpans(U64 bpawns) {return soutOne (soutFill(bpawns));} U64 wRearSpans (U64 wpawns) {return soutOne (soutFill(wpawns));} code
 * Pawns still member of their frontspan have at least one pawn behind on the same file.
 * Pawns still member of their rearspan have at least one pawn in front on the same file.
 * All pawns which are member of the opponent frontspans (or frontfill) have a **mechanical obstruction** and are **unfree**.

 =Interspans= The intersection of white and black frontspans is called interspan. Obviously interspans can only occur on closed files. Rooks on interspans may have a hard time, if the attacked opponent pawns are safe. Their vertical mobility is restricted and they may vulnerable to get trapped and attacked. On the other hand, if supported by other attacking pieces, there might be successful attacks against weak pawns and the especially the king. code white frontspan &  black frontspan  =  interspan 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 . . . 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     . . . . . . . . code  =Stop and Telestop= Stop squares are the push move targets of any pawn. code format="cpp" U64 wStop(U64 wpawns) {return nortOne (wpawns);} U64 bStop(U64 bpawns) {return soutOne (bpawns);} code Thus, the frontfills of the stop squares are the frontspans of the pawns: code format="cpp" U64 wFrontSpan(U64 wpawns) {return nortFill(wStop(wpawns));} U64 bFrontSpan(U64 bpawns) {return soutFill(bStop(bpawns));} code Telestop squares all the squares of the frontspan, except the stop squares code format="cpp" U64 wTeleStops(U64 wpawns) {return wFrontSpans(wStop(wpawns)) ^ wStop(wpawns);} U64 bTeleStops(U64 bpawns) {return bFrontSpans(bStop(bpawns)) ^ bStop(bpawns);} code

=See also=
 * Attack Spans
 * Fill Algorithms
 * Pawn Fills

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