:: Decomposing a Go Board into Cells
:: by Yatsuka Nakamura and Andrzej Trybulec
::
:: Received May 26, 1995
:: Copyright (c) 1995 Association of Mizar Users

begin

definition

let G be Matrix of (TOP-REAL 2);
let i be Nat;
func v_strip G,i -> Subset of (TOP-REAL 2) equals :Def1: :: GOBOARD5:def 1
{ |[r,s]| where r, s is Real : ( (G * i,1) `1 <= r & r <= (G * (i + 1),1) `1 ) } if ( 1 <= i & i < len G )
{ |[r,s]| where r, s is Real : (G * i,1) `1 <= r } if i >= len G
otherwise { |[r,s]| where r, s is Real : r <= (G * (i + 1),1) `1 } ;
coherence
( ( 1 <= i & i < len G implies { |[r,s]| where r, s is Real : ( (G * i,1) `1 <= r & r <= (G * (i + 1),1) `1 ) } is Subset of (TOP-REAL 2) ) & ( i >= len G implies { |[r,s]| where r, s is Real : (G * i,1) `1 <= r } is Subset of (TOP-REAL 2) ) & ( ( not 1 <= i or not i < len G ) & not i >= len G implies { |[r,s]| where r, s is Real : r <= (G * (i + 1),1) `1 } is Subset of (TOP-REAL 2) ) )

proof end;

correctness
consistency
for b₁ being Subset of (TOP-REAL 2) st 1 <= i & i < len G & i >= len G holds
( b₁ = { |[r,s]| where r, s is Real : ( (G * i,1) `1 <= r & r <= (G * (i + 1),1) `1 ) } iff b₁ = { |[r,s]| where r, s is Real : (G * i,1) `1 <= r } );
;
func h_strip G,i -> Subset of (TOP-REAL 2) equals :Def2: :: GOBOARD5:def 2
{ |[r,s]| where r, s is Real : ( (G * 1,i) `2 <= s & s <= (G * 1,(i + 1)) `2 ) } if ( 1 <= i & i < width G )
{ |[r,s]| where r, s is Real : (G * 1,i) `2 <= s } if i >= width G
otherwise { |[r,s]| where r, s is Real : s <= (G * 1,(i + 1)) `2 } ;
coherence
( ( 1 <= i & i < width G implies { |[r,s]| where r, s is Real : ( (G * 1,i) `2 <= s & s <= (G * 1,(i + 1)) `2 ) } is Subset of (TOP-REAL 2) ) & ( i >= width G implies { |[r,s]| where r, s is Real : (G * 1,i) `2 <= s } is Subset of (TOP-REAL 2) ) & ( ( not 1 <= i or not i < width G ) & not i >= width G implies { |[r,s]| where r, s is Real : s <= (G * 1,(i + 1)) `2 } is Subset of (TOP-REAL 2) ) )

proof end;

correctness
consistency
for b₁ being Subset of (TOP-REAL 2) st 1 <= i & i < width G & i >= width G holds
( b₁ = { |[r,s]| where r, s is Real : ( (G * 1,i) `2 <= s & s <= (G * 1,(i + 1)) `2 ) } iff b₁ = { |[r,s]| where r, s is Real : (G * 1,i) `2 <= s } );
;

end;

:: deftheorem Def1 defines v_strip GOBOARD5:def 1 :

for G being Matrix of (TOP-REAL 2)
for i being Nat holds
( ( 1 <= i & i < len G implies v_strip G,i = { |[r,s]| where r, s is Real : ( (G * i,1) `1 <= r & r <= (G * (i + 1),1) `1 ) } ) & ( i >= len G implies v_strip G,i = { |[r,s]| where r, s is Real : (G * i,1) `1 <= r } ) & ( ( not 1 <= i or not i < len G ) & not i >= len G implies v_strip G,i = { |[r,s]| where r, s is Real : r <= (G * (i + 1),1) `1 } ) );

:: deftheorem Def2 defines h_strip GOBOARD5:def 2 :

for G being Matrix of (TOP-REAL 2)
for i being Nat holds
( ( 1 <= i & i < width G implies h_strip G,i = { |[r,s]| where r, s is Real : ( (G * 1,i) `2 <= s & s <= (G * 1,(i + 1)) `2 ) } ) & ( i >= width G implies h_strip G,i = { |[r,s]| where r, s is Real : (G * 1,i) `2 <= s } ) & ( ( not 1 <= i or not i < width G ) & not i >= width G implies h_strip G,i = { |[r,s]| where r, s is Real : s <= (G * 1,(i + 1)) `2 } ) );

theorem :: GOBOARD5:1

canceled;

theorem Th2: :: GOBOARD5:2

for j, i being Element of NAT
for G being Matrix of (TOP-REAL 2) st G is Y_equal-in-column & 1 <= j & j <= width G & 1 <= i & i <= len G holds
(G * i,j) `2 = (G * 1,j) `2

proof end;

theorem Th3: :: GOBOARD5:3

for j, i being Element of NAT
for G being Matrix of (TOP-REAL 2) st G is X_equal-in-line & 1 <= j & j <= width G & 1 <= i & i <= len G holds
(G * i,j) `1 = (G * i,1) `1

proof end;

theorem Th4: :: GOBOARD5:4

for j, i1, i2 being Element of NAT
for G being Matrix of (TOP-REAL 2) st G is X_increasing-in-column & 1 <= j & j <= width G & 1 <= i1 & i1 < i2 & i2 <= len G holds
(G * i1,j) `1 < (G * i2,j) `1

proof end;

theorem Th5: :: GOBOARD5:5

for j1, j2, i being Element of NAT
for G being Matrix of (TOP-REAL 2) st G is Y_increasing-in-line & 1 <= j1 & j1 < j2 & j2 <= width G & 1 <= i & i <= len G holds
(G * i,j1) `2 < (G * i,j2) `2

proof end;

theorem Th6: :: GOBOARD5:6

for j, i being Element of NAT
for G being Matrix of (TOP-REAL 2) st G is Y_equal-in-column & 1 <= j & j < width G & 1 <= i & i <= len G holds
h_strip G,j = { |[r,s]| where r, s is Real : ( (G * i,j) `2 <= s & s <= (G * i,(j + 1)) `2 ) }

proof end;

theorem Th7: :: GOBOARD5:7

for i being Element of NAT
for G being Matrix of (TOP-REAL 2) st not G is empty-yielding & G is Y_equal-in-column & 1 <= i & i <= len G holds
h_strip G,(width G) = { |[r,s]| where r, s is Real : (G * i,(width G)) `2 <= s }

proof end;

theorem Th8: :: GOBOARD5:8

for i being Element of NAT
for G being Matrix of (TOP-REAL 2) st not G is empty-yielding & G is Y_equal-in-column & 1 <= i & i <= len G holds
h_strip G,0 = { |[r,s]| where r, s is Real : s <= (G * i,1) `2 }

proof end;

theorem Th9: :: GOBOARD5:9

for i, j being Element of NAT
for G being Matrix of (TOP-REAL 2) st G is X_equal-in-line & 1 <= i & i < len G & 1 <= j & j <= width G holds
v_strip G,i = { |[r,s]| where r, s is Real : ( (G * i,j) `1 <= r & r <= (G * (i + 1),j) `1 ) }

proof end;

theorem Th10: :: GOBOARD5:10

for j being Element of NAT
for G being Matrix of (TOP-REAL 2) st not G is empty-yielding & G is X_equal-in-line & 1 <= j & j <= width G holds
v_strip G,(len G) = { |[r,s]| where r, s is Real : (G * (len G),j) `1 <= r }

proof end;

theorem Th11: :: GOBOARD5:11

for j being Element of NAT
for G being Matrix of (TOP-REAL 2) st not G is empty-yielding & G is X_equal-in-line & 1 <= j & j <= width G holds
v_strip G,0 = { |[r,s]| where r, s is Real : r <= (G * 1,j) `1 }

proof end;

definition

let G be Matrix of (TOP-REAL 2);
let i, j be Nat;
func cell G,i,j -> Subset of (TOP-REAL 2) equals :: GOBOARD5:def 3
(v_strip G,i) /\ (h_strip G,j);
correctness
coherence
(v_strip G,i) /\ (h_strip G,j) is Subset of (TOP-REAL 2);
;

end;

:: deftheorem defines cell GOBOARD5:def 3 :

for G being Matrix of (TOP-REAL 2)
for i, j being Nat holds cell G,i,j = (v_strip G,i) /\ (h_strip G,j);

definition

let IT be FinSequence of (TOP-REAL 2);
attr IT is s.c.c. means :: GOBOARD5:def 4
for i, j being Element of NAT st i + 1 < j & ( ( i > 1 & j < len IT ) or j + 1 < len IT ) holds
LSeg IT,i misses LSeg IT,j;

end;

:: deftheorem defines s.c.c. GOBOARD5:def 4 :

for IT being FinSequence of (TOP-REAL 2) holds
( IT is s.c.c. iff for i, j being Element of NAT st i + 1 < j & ( ( i > 1 & j < len IT ) or j + 1 < len IT ) holds
LSeg IT,i misses LSeg IT,j );

definition

let IT be non empty FinSequence of (TOP-REAL 2);
attr IT is standard means :Def5: :: GOBOARD5:def 5
IT is_sequence_on GoB IT;

end;

:: deftheorem Def5 defines standard GOBOARD5:def 5 :

for IT being non empty FinSequence of (TOP-REAL 2) holds
( IT is standard iff IT is_sequence_on GoB IT );

registration

cluster V1() V4( NAT ) V5(the carrier of (TOP-REAL 2)) Function-like non constant non empty V29() FinSequence-like FinSubsequence-like circular special unfolded s.c.c. standard FinSequence of the carrier of (TOP-REAL 2);
existence
ex b₁ being non empty FinSequence of (TOP-REAL 2) st
( not b₁ is constant & b₁ is special & b₁ is unfolded & b₁ is circular & b₁ is s.c.c. & b₁ is standard )

proof end;

end;

Lm1: for f being FinSequence of (TOP-REAL 2) holds dom (X_axis f) = dom f

proof end;

Lm2: for f being FinSequence of (TOP-REAL 2) holds dom (Y_axis f) = dom f

proof end;

theorem Th12: :: GOBOARD5:12

for f being non empty FinSequence of (TOP-REAL 2)
for n being Element of NAT st n in dom f holds
ex i, j being Element of NAT st
( [i,j] in Indices (GoB f) & f /. n = (GoB f) * i,j )

proof end;

theorem Th13: :: GOBOARD5:13

for f being non empty standard FinSequence of (TOP-REAL 2)
for n being Element of NAT st n in dom f & n + 1 in dom f holds
for m, k, i, j being Element of NAT st [m,k] in Indices (GoB f) & [i,j] in Indices (GoB f) & f /. n = (GoB f) * m,k & f /. (n + 1) = (GoB f) * i,j holds
(abs (m - i)) + (abs (k - j)) = 1

proof end;

definition

mode special_circular_sequence is non empty circular special unfolded s.c.c. FinSequence of (TOP-REAL 2);

end;

definition

let f be standard special_circular_sequence;
let k be Element of NAT ;
assume that
A1: 1 <= k and
A2: k + 1 <= len f ;
k <= k + 1 by NAT_1:11;
then k <= len f by A2, XXREAL_0:2;
then A3: k in dom f by A1, FINSEQ_3:27;
then consider i1, j1 being Element of NAT such that
A4: [i1,j1] in Indices (GoB f) and
A5: f /. k = (GoB f) * i1,j1 by Th12;
k + 1 >= 1 by NAT_1:11;
then A6: k + 1 in dom f by A2, FINSEQ_3:27;
then consider i2, j2 being Element of NAT such that
A7: [i2,j2] in Indices (GoB f) and
A8: f /. (k + 1) = (GoB f) * i2,j2 by Th12;
A9: (abs (i1 - i2)) + (abs (j1 - j2)) = 1 by A3, A4, A5, A6, A7, A8, Th13;

A10: now

per cases ( ( abs (i1 - i2) = 1 & j1 = j2 ) or ( i1 = i2 & abs (j1 - j2) = 1 ) ) by A9, GOBOARD1:2;

case that A11: abs (i1 - i2) = 1 and
A12: j1 = j2 ; :: thesis: ( ( i1 = i2 + 1 or i1 + 1 = i2 ) & j1 = j2 )

( i1 - i2 = 1 or - (i1 - i2) = 1 ) by A11, ABSVALUE:def 1;
hence ( i1 = i2 + 1 or i1 + 1 = i2 ) ; :: thesis: j1 = j2
thus j1 = j2 by A12; :: thesis: verum

end;

case that A13: i1 = i2 and
A14: abs (j1 - j2) = 1 ; :: thesis: ( ( j1 = j2 + 1 or j1 + 1 = j2 ) & i1 = i2 )

( j1 - j2 = 1 or - (j1 - j2) = 1 ) by A14, ABSVALUE:def 1;
hence ( j1 = j2 + 1 or j1 + 1 = j2 ) ; :: thesis: i1 = i2
thus i1 = i2 by A13; :: thesis: verum

end;

end;

end;

func right_cell f,k -> Subset of (TOP-REAL 2) means :Def6: :: GOBOARD5:def 6
for i1, j1, i2, j2 being Element of NAT st [i1,j1] in Indices (GoB f) & [i2,j2] in Indices (GoB f) & f /. k = (GoB f) * i1,j1 & f /. (k + 1) = (GoB f) * i2,j2 & not ( i1 = i2 & j1 + 1 = j2 & it = cell (GoB f),i1,j1 ) & not ( i1 + 1 = i2 & j1 = j2 & it = cell (GoB f),i1,(j1 -' 1) ) & not ( i1 = i2 + 1 & j1 = j2 & it = cell (GoB f),i2,j2 ) holds
( i1 = i2 & j1 = j2 + 1 & it = cell (GoB f),(i1 -' 1),j2 );
existence
ex b₁ being Subset of (TOP-REAL 2) st
for i1, j1, i2, j2 being Element of NAT st [i1,j1] in Indices (GoB f) & [i2,j2] in Indices (GoB f) & f /. k = (GoB f) * i1,j1 & f /. (k + 1) = (GoB f) * i2,j2 & not ( i1 = i2 & j1 + 1 = j2 & b₁ = cell (GoB f),i1,j1 ) & not ( i1 + 1 = i2 & j1 = j2 & b₁ = cell (GoB f),i1,(j1 -' 1) ) & not ( i1 = i2 + 1 & j1 = j2 & b₁ = cell (GoB f),i2,j2 ) holds
( i1 = i2 & j1 = j2 + 1 & b₁ = cell (GoB f),(i1 -' 1),j2 )

proof end;

uniqueness
for b₁, b₂ being Subset of (TOP-REAL 2) st ( for i1, j1, i2, j2 being Element of NAT st [i1,j1] in Indices (GoB f) & [i2,j2] in Indices (GoB f) & f /. k = (GoB f) * i1,j1 & f /. (k + 1) = (GoB f) * i2,j2 & not ( i1 = i2 & j1 + 1 = j2 & b₁ = cell (GoB f),i1,j1 ) & not ( i1 + 1 = i2 & j1 = j2 & b₁ = cell (GoB f),i1,(j1 -' 1) ) & not ( i1 = i2 + 1 & j1 = j2 & b₁ = cell (GoB f),i2,j2 ) holds
( i1 = i2 & j1 = j2 + 1 & b₁ = cell (GoB f),(i1 -' 1),j2 ) ) & ( for i1, j1, i2, j2 being Element of NAT st [i1,j1] in Indices (GoB f) & [i2,j2] in Indices (GoB f) & f /. k = (GoB f) * i1,j1 & f /. (k + 1) = (GoB f) * i2,j2 & not ( i1 = i2 & j1 + 1 = j2 & b₂ = cell (GoB f),i1,j1 ) & not ( i1 + 1 = i2 & j1 = j2 & b₂ = cell (GoB f),i1,(j1 -' 1) ) & not ( i1 = i2 + 1 & j1 = j2 & b₂ = cell (GoB f),i2,j2 ) holds
( i1 = i2 & j1 = j2 + 1 & b₂ = cell (GoB f),(i1 -' 1),j2 ) ) holds
b₁ = b₂

proof end;

func left_cell f,k -> Subset of (TOP-REAL 2) means :Def7: :: GOBOARD5:def 7
for i1, j1, i2, j2 being Element of NAT st [i1,j1] in Indices (GoB f) & [i2,j2] in Indices (GoB f) & f /. k = (GoB f) * i1,j1 & f /. (k + 1) = (GoB f) * i2,j2 & not ( i1 = i2 & j1 + 1 = j2 & it = cell (GoB f),(i1 -' 1),j1 ) & not ( i1 + 1 = i2 & j1 = j2 & it = cell (GoB f),i1,j1 ) & not ( i1 = i2 + 1 & j1 = j2 & it = cell (GoB f),i2,(j2 -' 1) ) holds
( i1 = i2 & j1 = j2 + 1 & it = cell (GoB f),i1,j2 );
existence
ex b₁ being Subset of (TOP-REAL 2) st
for i1, j1, i2, j2 being Element of NAT st [i1,j1] in Indices (GoB f) & [i2,j2] in Indices (GoB f) & f /. k = (GoB f) * i1,j1 & f /. (k + 1) = (GoB f) * i2,j2 & not ( i1 = i2 & j1 + 1 = j2 & b₁ = cell (GoB f),(i1 -' 1),j1 ) & not ( i1 + 1 = i2 & j1 = j2 & b₁ = cell (GoB f),i1,j1 ) & not ( i1 = i2 + 1 & j1 = j2 & b₁ = cell (GoB f),i2,(j2 -' 1) ) holds
( i1 = i2 & j1 = j2 + 1 & b₁ = cell (GoB f),i1,j2 )

proof end;

uniqueness
for b₁, b₂ being Subset of (TOP-REAL 2) st ( for i1, j1, i2, j2 being Element of NAT st [i1,j1] in Indices (GoB f) & [i2,j2] in Indices (GoB f) & f /. k = (GoB f) * i1,j1 & f /. (k + 1) = (GoB f) * i2,j2 & not ( i1 = i2 & j1 + 1 = j2 & b₁ = cell (GoB f),(i1 -' 1),j1 ) & not ( i1 + 1 = i2 & j1 = j2 & b₁ = cell (GoB f),i1,j1 ) & not ( i1 = i2 + 1 & j1 = j2 & b₁ = cell (GoB f),i2,(j2 -' 1) ) holds
( i1 = i2 & j1 = j2 + 1 & b₁ = cell (GoB f),i1,j2 ) ) & ( for i1, j1, i2, j2 being Element of NAT st [i1,j1] in Indices (GoB f) & [i2,j2] in Indices (GoB f) & f /. k = (GoB f) * i1,j1 & f /. (k + 1) = (GoB f) * i2,j2 & not ( i1 = i2 & j1 + 1 = j2 & b₂ = cell (GoB f),(i1 -' 1),j1 ) & not ( i1 + 1 = i2 & j1 = j2 & b₂ = cell (GoB f),i1,j1 ) & not ( i1 = i2 + 1 & j1 = j2 & b₂ = cell (GoB f),i2,(j2 -' 1) ) holds
( i1 = i2 & j1 = j2 + 1 & b₂ = cell (GoB f),i1,j2 ) ) holds
b₁ = b₂

proof end;

end;

:: deftheorem Def6 defines right_cell GOBOARD5:def 6 :

for f being standard special_circular_sequence
for k being Element of NAT st 1 <= k & k + 1 <= len f holds
for b₃ being Subset of (TOP-REAL 2) holds
( b₃ = right_cell f,k iff for i1, j1, i2, j2 being Element of NAT st [i1,j1] in Indices (GoB f) & [i2,j2] in Indices (GoB f) & f /. k = (GoB f) * i1,j1 & f /. (k + 1) = (GoB f) * i2,j2 & not ( i1 = i2 & j1 + 1 = j2 & b₃ = cell (GoB f),i1,j1 ) & not ( i1 + 1 = i2 & j1 = j2 & b₃ = cell (GoB f),i1,(j1 -' 1) ) & not ( i1 = i2 + 1 & j1 = j2 & b₃ = cell (GoB f),i2,j2 ) holds
( i1 = i2 & j1 = j2 + 1 & b₃ = cell (GoB f),(i1 -' 1),j2 ) );

:: deftheorem Def7 defines left_cell GOBOARD5:def 7 :

for f being standard special_circular_sequence
for k being Element of NAT st 1 <= k & k + 1 <= len f holds
for b₃ being Subset of (TOP-REAL 2) holds
( b₃ = left_cell f,k iff for i1, j1, i2, j2 being Element of NAT st [i1,j1] in Indices (GoB f) & [i2,j2] in Indices (GoB f) & f /. k = (GoB f) * i1,j1 & f /. (k + 1) = (GoB f) * i2,j2 & not ( i1 = i2 & j1 + 1 = j2 & b₃ = cell (GoB f),(i1 -' 1),j1 ) & not ( i1 + 1 = i2 & j1 = j2 & b₃ = cell (GoB f),i1,j1 ) & not ( i1 = i2 + 1 & j1 = j2 & b₃ = cell (GoB f),i2,(j2 -' 1) ) holds
( i1 = i2 & j1 = j2 + 1 & b₃ = cell (GoB f),i1,j2 ) );

theorem Th14: :: GOBOARD5:14

for i, j being Element of NAT
for G being Matrix of (TOP-REAL 2) st not G is empty-yielding & G is X_equal-in-line & G is X_increasing-in-column & i < len G & 1 <= j & j < width G holds
LSeg (G * (i + 1),j),(G * (i + 1),(j + 1)) c= v_strip G,i

proof end;

theorem Th15: :: GOBOARD5:15

for i, j being Element of NAT
for G being Matrix of (TOP-REAL 2) st not G is empty-yielding & G is X_equal-in-line & G is X_increasing-in-column & 1 <= i & i <= len G & 1 <= j & j < width G holds
LSeg (G * i,j),(G * i,(j + 1)) c= v_strip G,i

proof end;

theorem Th16: :: GOBOARD5:16

for j, i being Element of NAT
for G being Matrix of (TOP-REAL 2) st not G is empty-yielding & G is Y_equal-in-column & G is Y_increasing-in-line & j < width G & 1 <= i & i < len G holds
LSeg (G * i,(j + 1)),(G * (i + 1),(j + 1)) c= h_strip G,j

proof end;

theorem Th17: :: GOBOARD5:17

for j, i being Element of NAT
for G being Matrix of (TOP-REAL 2) st not G is empty-yielding & G is Y_equal-in-column & G is Y_increasing-in-line & 1 <= j & j <= width G & 1 <= i & i < len G holds
LSeg (G * i,j),(G * (i + 1),j) c= h_strip G,j

proof end;

theorem Th18: :: GOBOARD5:18

for i, j being Element of NAT
for G being Matrix of (TOP-REAL 2) st G is Y_equal-in-column & G is Y_increasing-in-line & 1 <= i & i <= len G & 1 <= j & j + 1 <= width G holds
LSeg (G * i,j),(G * i,(j + 1)) c= h_strip G,j

proof end;

theorem Th19: :: GOBOARD5:19

for i, j being Element of NAT
for G being Go-board st i < len G & 1 <= j & j < width G holds
LSeg (G * (i + 1),j),(G * (i + 1),(j + 1)) c= cell G,i,j

proof end;

theorem Th20: :: GOBOARD5:20

for i, j being Element of NAT
for G being Go-board st 1 <= i & i <= len G & 1 <= j & j < width G holds
LSeg (G * i,j),(G * i,(j + 1)) c= cell G,i,j

proof end;

theorem Th21: :: GOBOARD5:21

for j, i being Element of NAT
for G being Matrix of (TOP-REAL 2) st G is X_equal-in-line & G is X_increasing-in-column & 1 <= j & j <= width G & 1 <= i & i + 1 <= len G holds
LSeg (G * i,j),(G * (i + 1),j) c= v_strip G,i

proof end;

theorem Th22: :: GOBOARD5:22

for j, i being Element of NAT
for G being Go-board st j < width G & 1 <= i & i < len G holds
LSeg (G * i,(j + 1)),(G * (i + 1),(j + 1)) c= cell G,i,j

proof end;

theorem Th23: :: GOBOARD5:23

for i, j being Element of NAT
for G being Go-board st 1 <= i & i < len G & 1 <= j & j <= width G holds
LSeg (G * i,j),(G * (i + 1),j) c= cell G,i,j

proof end;

theorem Th24: :: GOBOARD5:24

for i being Element of NAT
for G being Matrix of (TOP-REAL 2) st not G is empty-yielding & G is X_equal-in-line & G is X_increasing-in-column & i + 1 <= len G holds
(v_strip G,i) /\ (v_strip G,(i + 1)) = { q where q is Point of (TOP-REAL 2) : q `1 = (G * (i + 1),1) `1 }

proof end;

theorem Th25: :: GOBOARD5:25

for j being Element of NAT
for G being Matrix of (TOP-REAL 2) st not G is empty-yielding & G is Y_equal-in-column & G is Y_increasing-in-line & j + 1 <= width G holds
(h_strip G,j) /\ (h_strip G,(j + 1)) = { q where q is Point of (TOP-REAL 2) : q `2 = (G * 1,(j + 1)) `2 }

proof end;

theorem Th26: :: GOBOARD5:26

for i, j being Element of NAT
for G being Go-board st i < len G & 1 <= j & j < width G holds
(cell G,i,j) /\ (cell G,(i + 1),j) = LSeg (G * (i + 1),j),(G * (i + 1),(j + 1))

proof end;

theorem Th27: :: GOBOARD5:27

for j, i being Element of NAT
for G being Go-board st j < width G & 1 <= i & i < len G holds
(cell G,i,j) /\ (cell G,i,(j + 1)) = LSeg (G * i,(j + 1)),(G * (i + 1),(j + 1))

proof end;

theorem Th28: :: GOBOARD5:28

for k, i, j being Element of NAT
for f being standard special_circular_sequence st 1 <= k & k + 1 <= len f & [(i + 1),j] in Indices (GoB f) & [(i + 1),(j + 1)] in Indices (GoB f) & f /. k = (GoB f) * (i + 1),j & f /. (k + 1) = (GoB f) * (i + 1),(j + 1) holds
( left_cell f,k = cell (GoB f),i,j & right_cell f,k = cell (GoB f),(i + 1),j )

proof end;

theorem Th29: :: GOBOARD5:29

for k, i, j being Element of NAT
for f being standard special_circular_sequence st 1 <= k & k + 1 <= len f & [i,(j + 1)] in Indices (GoB f) & [(i + 1),(j + 1)] in Indices (GoB f) & f /. k = (GoB f) * i,(j + 1) & f /. (k + 1) = (GoB f) * (i + 1),(j + 1) holds
( left_cell f,k = cell (GoB f),i,(j + 1) & right_cell f,k = cell (GoB f),i,j )

proof end;

theorem Th30: :: GOBOARD5:30

for k, i, j being Element of NAT
for f being standard special_circular_sequence st 1 <= k & k + 1 <= len f & [i,(j + 1)] in Indices (GoB f) & [(i + 1),(j + 1)] in Indices (GoB f) & f /. k = (GoB f) * (i + 1),(j + 1) & f /. (k + 1) = (GoB f) * i,(j + 1) holds
( left_cell f,k = cell (GoB f),i,j & right_cell f,k = cell (GoB f),i,(j + 1) )

proof end;

theorem Th31: :: GOBOARD5:31

for k, i, j being Element of NAT
for f being standard special_circular_sequence st 1 <= k & k + 1 <= len f & [(i + 1),(j + 1)] in Indices (GoB f) & [(i + 1),j] in Indices (GoB f) & f /. k = (GoB f) * (i + 1),(j + 1) & f /. (k + 1) = (GoB f) * (i + 1),j holds
( left_cell f,k = cell (GoB f),(i + 1),j & right_cell f,k = cell (GoB f),i,j )

proof end;

theorem :: GOBOARD5:32

for k being Element of NAT
for f being standard special_circular_sequence st 1 <= k & k + 1 <= len f holds
(left_cell f,k) /\ (right_cell f,k) = LSeg f,k

proof end;