let C be non empty compact non horizontal non vertical Subset of (TOP-REAL 2); :: thesis: for n being Element of NAT
for f being FinSequence of (TOP-REAL 2) st f is_sequence_on Gauge C,n & len f > 1 holds
for i1, j1 being Element of NAT st front_left_cell f,((len f) -' 1),(Gauge C,n) meets C & [i1,j1] in Indices (Gauge C,n) & f /. ((len f) -' 1) = (Gauge C,n) * i1,j1 & [(i1 + 1),j1] in Indices (Gauge C,n) & f /. (len f) = (Gauge C,n) * (i1 + 1),j1 holds
[(i1 + 2),j1] in Indices (Gauge C,n)
let n be Element of NAT ; :: thesis: for f being FinSequence of (TOP-REAL 2) st f is_sequence_on Gauge C,n & len f > 1 holds
for i1, j1 being Element of NAT st front_left_cell f,((len f) -' 1),(Gauge C,n) meets C & [i1,j1] in Indices (Gauge C,n) & f /. ((len f) -' 1) = (Gauge C,n) * i1,j1 & [(i1 + 1),j1] in Indices (Gauge C,n) & f /. (len f) = (Gauge C,n) * (i1 + 1),j1 holds
[(i1 + 2),j1] in Indices (Gauge C,n)
set G = Gauge C,n;
A1: len (Gauge C,n) = width (Gauge C,n) by JORDAN8:def 1;
let f be FinSequence of (TOP-REAL 2); :: thesis: ( f is_sequence_on Gauge C,n & len f > 1 implies for i1, j1 being Element of NAT st front_left_cell f,((len f) -' 1),(Gauge C,n) meets C & [i1,j1] in Indices (Gauge C,n) & f /. ((len f) -' 1) = (Gauge C,n) * i1,j1 & [(i1 + 1),j1] in Indices (Gauge C,n) & f /. (len f) = (Gauge C,n) * (i1 + 1),j1 holds
[(i1 + 2),j1] in Indices (Gauge C,n) )
assume that
A2: f is_sequence_on Gauge C,n and
A3: len f > 1 ; :: thesis: for i1, j1 being Element of NAT st front_left_cell f,((len f) -' 1),(Gauge C,n) meets C & [i1,j1] in Indices (Gauge C,n) & f /. ((len f) -' 1) = (Gauge C,n) * i1,j1 & [(i1 + 1),j1] in Indices (Gauge C,n) & f /. (len f) = (Gauge C,n) * (i1 + 1),j1 holds
[(i1 + 2),j1] in Indices (Gauge C,n)
let i1, j1 be Element of NAT ; :: thesis: ( front_left_cell f,((len f) -' 1),(Gauge C,n) meets C & [i1,j1] in Indices (Gauge C,n) & f /. ((len f) -' 1) = (Gauge C,n) * i1,j1 & [(i1 + 1),j1] in Indices (Gauge C,n) & f /. (len f) = (Gauge C,n) * (i1 + 1),j1 implies [(i1 + 2),j1] in Indices (Gauge C,n) )
assume that
A4: front_left_cell f,((len f) -' 1),(Gauge C,n) meets C and
A5: ( [i1,j1] in Indices (Gauge C,n) & f /. ((len f) -' 1) = (Gauge C,n) * i1,j1 ) and
A6: ( [(i1 + 1),j1] in Indices (Gauge C,n) & f /. (len f) = (Gauge C,n) * (i1 + 1),j1 ) ; :: thesis: [(i1 + 2),j1] in Indices (Gauge C,n)
A7: 1 <= (len f) -' 1 by A3, NAT_D:49;
A8: ((len f) -' 1) + 1 = len f by A3, XREAL_1:237;
A9: ( 1 <= i1 + 1 & i1 + 1 <= len (Gauge C,n) & 1 <= j1 & j1 <= width (Gauge C,n) ) by A6, MATRIX_1:39;
A10: ( 1 <= (i1 + 1) + 1 & 1 <= j1 + 1 ) by NAT_1:12;

now

assume (i1 + 1) + 1 > len (Gauge C,n) ; :: thesis: contradiction
then ( (i1 + 1) + 1 <= (len (Gauge C,n)) + 1 & (len (Gauge C,n)) + 1 <= (i1 + 1) + 1 ) by A9, NAT_1:13, XREAL_1:8;
then (i1 + 1) + 1 = (len (Gauge C,n)) + 1 by XXREAL_0:1;
then cell (Gauge C,n),(len (Gauge C,n)),j1 meets C by A2, A4, A5, A6, A7, A8, GOBRD13:37;
hence contradiction by A1, A9, JORDAN8:19; :: thesis: verum

end;

hence [(i1 + 2),j1] in Indices (Gauge C,n) by A9, A10, MATRIX_1:37; :: thesis: verum