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, j2 being Element of NAT st front_right_cell f,((len f) -' 1),(Gauge C,n) meets C & [i1,(j2 + 1)] in Indices (Gauge C,n) & f /. ((len f) -' 1) = (Gauge C,n) * i1,(j2 + 1) & [i1,j2] in Indices (Gauge C,n) & f /. (len f) = (Gauge C,n) * i1,j2 holds
[(i1 -' 1),j2] 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, j2 being Element of NAT st front_right_cell f,((len f) -' 1),(Gauge C,n) meets C & [i1,(j2 + 1)] in Indices (Gauge C,n) & f /. ((len f) -' 1) = (Gauge C,n) * i1,(j2 + 1) & [i1,j2] in Indices (Gauge C,n) & f /. (len f) = (Gauge C,n) * i1,j2 holds
[(i1 -' 1),j2] 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, j2 being Element of NAT st front_right_cell f,((len f) -' 1),(Gauge C,n) meets C & [i1,(j2 + 1)] in Indices (Gauge C,n) & f /. ((len f) -' 1) = (Gauge C,n) * i1,(j2 + 1) & [i1,j2] in Indices (Gauge C,n) & f /. (len f) = (Gauge C,n) * i1,j2 holds
[(i1 -' 1),j2] in Indices (Gauge C,n) )
assume that
A2: f is_sequence_on Gauge C,n and
A3: len f > 1 ; :: thesis: for i1, j2 being Element of NAT st front_right_cell f,((len f) -' 1),(Gauge C,n) meets C & [i1,(j2 + 1)] in Indices (Gauge C,n) & f /. ((len f) -' 1) = (Gauge C,n) * i1,(j2 + 1) & [i1,j2] in Indices (Gauge C,n) & f /. (len f) = (Gauge C,n) * i1,j2 holds
[(i1 -' 1),j2] in Indices (Gauge C,n)
let i1, j2 be Element of NAT ; :: thesis: ( front_right_cell f,((len f) -' 1),(Gauge C,n) meets C & [i1,(j2 + 1)] in Indices (Gauge C,n) & f /. ((len f) -' 1) = (Gauge C,n) * i1,(j2 + 1) & [i1,j2] in Indices (Gauge C,n) & f /. (len f) = (Gauge C,n) * i1,j2 implies [(i1 -' 1),j2] in Indices (Gauge C,n) )
assume that
A4: front_right_cell f,((len f) -' 1),(Gauge C,n) meets C and
A5: ( [i1,(j2 + 1)] in Indices (Gauge C,n) & f /. ((len f) -' 1) = (Gauge C,n) * i1,(j2 + 1) ) and
A6: ( [i1,j2] in Indices (Gauge C,n) & f /. (len f) = (Gauge C,n) * i1,j2 ) ; :: thesis: [(i1 -' 1),j2] 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 & i1 <= len (Gauge C,n) & 1 <= j2 & j2 <= width (Gauge C,n) ) by A6, MATRIX_1:39;
then A10: ( i1 -' 1 <= len (Gauge C,n) & j2 -' 1 <= width (Gauge C,n) ) by NAT_D:44;

now

assume i1 -' 1 < 1 ; :: thesis: contradiction
then i1 <= 1 by NAT_1:14, NAT_D:36;
then i1 = 1 by A9, XXREAL_0:1;
then cell (Gauge C,n),(1 -' 1),(j2 -' 1) meets C by A2, A4, A5, A6, A7, A8, GOBRD13:42;
then cell (Gauge C,n),0 ,(j2 -' 1) meets C by XREAL_1:234;
hence contradiction by A1, A9, JORDAN8:21, NAT_D:44; :: thesis: verum

end;

hence [(i1 -' 1),j2] in Indices (Gauge C,n) by A9, A10, MATRIX_1:37; :: thesis: verum