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 j1, i2 being Element of NAT st left_cell f,((len f) -' 1),(Gauge C,n) meets C & [(i2 + 1),j1] in Indices (Gauge C,n) & f /. ((len f) -' 1) = (Gauge C,n) * (i2 + 1),j1 & [i2,j1] in Indices (Gauge C,n) & f /. (len f) = (Gauge C,n) * i2,j1 holds
[i2,(j1 -' 1)] 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 j1, i2 being Element of NAT st left_cell f,((len f) -' 1),(Gauge C,n) meets C & [(i2 + 1),j1] in Indices (Gauge C,n) & f /. ((len f) -' 1) = (Gauge C,n) * (i2 + 1),j1 & [i2,j1] in Indices (Gauge C,n) & f /. (len f) = (Gauge C,n) * i2,j1 holds
[i2,(j1 -' 1)] in Indices (Gauge C,n)

set G = Gauge C,n;
let f be FinSequence of (TOP-REAL 2); :: thesis: ( f is_sequence_on Gauge C,n & len f > 1 implies for j1, i2 being Element of NAT st left_cell f,((len f) -' 1),(Gauge C,n) meets C & [(i2 + 1),j1] in Indices (Gauge C,n) & f /. ((len f) -' 1) = (Gauge C,n) * (i2 + 1),j1 & [i2,j1] in Indices (Gauge C,n) & f /. (len f) = (Gauge C,n) * i2,j1 holds
[i2,(j1 -' 1)] in Indices (Gauge C,n) )

assume that
A1: f is_sequence_on Gauge C,n and
A2: len f > 1 ; :: thesis: for j1, i2 being Element of NAT st left_cell f,((len f) -' 1),(Gauge C,n) meets C & [(i2 + 1),j1] in Indices (Gauge C,n) & f /. ((len f) -' 1) = (Gauge C,n) * (i2 + 1),j1 & [i2,j1] in Indices (Gauge C,n) & f /. (len f) = (Gauge C,n) * i2,j1 holds
[i2,(j1 -' 1)] in Indices (Gauge C,n)

A3: ( 1 <= (len f) -' 1 & ((len f) -' 1) + 1 = len f ) by A2, NAT_D:49, XREAL_1:237;
let j1, i2 be Element of NAT ; :: thesis: ( left_cell f,((len f) -' 1),(Gauge C,n) meets C & [(i2 + 1),j1] in Indices (Gauge C,n) & f /. ((len f) -' 1) = (Gauge C,n) * (i2 + 1),j1 & [i2,j1] in Indices (Gauge C,n) & f /. (len f) = (Gauge C,n) * i2,j1 implies [i2,(j1 -' 1)] in Indices (Gauge C,n) )
assume that
A4: ( left_cell f,((len f) -' 1),(Gauge C,n) meets C & [(i2 + 1),j1] in Indices (Gauge C,n) & f /. ((len f) -' 1) = (Gauge C,n) * (i2 + 1),j1 ) and
A5: [i2,j1] in Indices (Gauge C,n) and
A6: f /. (len f) = (Gauge C,n) * i2,j1 ; :: thesis: [i2,(j1 -' 1)] in Indices (Gauge C,n)
A7: i2 <= len (Gauge C,n) by A5, MATRIX_1:39;
A8: 1 <= j1 by A5, MATRIX_1:39;
A9: now end;
A10: j1 -' 1 <= j1 by NAT_D:35;
j1 <= width (Gauge C,n) by A5, MATRIX_1:39;
then A11: j1 -' 1 <= width (Gauge C,n) by A10, XXREAL_0:2;
1 <= i2 by A5, MATRIX_1:39;
hence [i2,(j1 -' 1)] in Indices (Gauge C,n) by A7, A11, A9, MATRIX_1:37; :: thesis: verum