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Set-wise pattern, based on attackspans are for instance isolated pawns, passers and candidates.

The admittedly arbitrary definition of front attackspans includes the attacked squares itself, thus it is like a fill of attacked squares in the appropriate direction. The rear attackspan is the complement set on the same file, so that the union of both spans covers the whole file. As always, we keep disjoint east-west sets for separate applications, despite illustrated as union with one single pawn:

white attack        white attack     attack filefill with least one
frontspan           rearspan         square attacked by white
. . 1 . 1 . . .     . . . . . . . .     . . 1 . 1 . . .
. . 1 . 1 . . .     . . . . . . . .     . . 1 . 1 . . .
. . 1 . 1 . . .     . . . . . . . .     . . 1 . 1 . . .
. . 1 . 1 . . .     . . . . . . . .     . . 1 . 1 . . .
. . . w . . . .     . . 1 w 1 . . .     . . 1 w 1 . . .
. . . . . . . .     . . 1 . 1 . . .     . . 1 . 1 . . .
. . . . . . . .     . . 1 . 1 . . .     . . 1 . 1 . . .
. . . . . . . .     . . 1 . 1 . . .     . . 1 . 1 . . .
 
black attack        black attack     attack filefill with least one
frontspan           rearspan         square attacked by black
. . . . . . . .     . . 1 . 1 . . .     . . 1 . 1 . . .
. . . . . . . .     . . 1 . 1 . . .     . . 1 . 1 . . .
. . . . . . . .     . . 1 . 1 . . .     . . 1 . 1 . . .
. . . . . . . .     . . 1 . 1 . . .     . . 1 . 1 . . .
. . . b . . . .     . . 1 b 1 . . .     . . 1 b 1 . . .
. . 1 . 1 . . .     . . . . . . . .     . . 1 . 1 . . .
. . 1 . 1 . . .     . . . . . . . .     . . 1 . 1 . . .
. . 1 . 1 . . .     . . . . . . . .     . . 1 . 1 . . .

The routines based on one step only, vertical fills and pawn spans :

U64 wEastAttackFrontSpans (U64 wpawns) {return eastOne(wFrontSpans(wpawns));}
U64 wWestAttackFrontSpans (U64 wpawns) {return westOne(wFrontSpans(wpawns));}
U64 bEastAttackFrontSpans (U64 bpawns) {return eastOne(bFrontSpans(bpawns));}
U64 bWestAttackFrontSpans (U64 bpawns) {return westOne(bFrontSpans(bpawns));}
 
U64 wEastAttackRearSpans (U64 wpawns)  {return eastOne(wRearFill(wpawns));}
U64 wWestAttackRearSpans (U64 wpawns)  {return westOne(wRearFill(wpawns));}
U64 bEastAttackRearSpans (U64 bpawns)  {return eastOne(bRearFill(bpawns));}
U64 bWestAttackRearSpans (U64 bpawns)  {return westOne(bRearFill(bpawns));}

The filefills are independent on color

U64 eastAttackFileFill (U64 pawns) {return eastOne(fileFill(pawns));}
U64 westAttackFileFill (U64 pawns) {return westOne(fileFill(pawns));}

• If a pawn is not member of own west or east attack filefills, the pawn is half-isolated.
• If a pawn is not member of the union of own east and west attack filefills, the pawn is isolated.
• If a pawn is not member of the union of all opponent front pawn- and attack-spans, it is a passed pawn.

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