let n, i, j be Nat; :: thesis: for K being Field
for a being Element of K
for R being FinSequence_of_Square-Matrix of K
for A being Matrix of n,K st i in dom A & j in Seg n holds
Deleting (block_diagonal (R ^ <*A*>),a),(i + (Sum (Len R))),(j + (Sum (Len R))) = block_diagonal (R ^ <*(Deleting A,i,j)*>),a

let K be Field; :: thesis: for a being Element of K
for R being FinSequence_of_Square-Matrix of K
for A being Matrix of n,K st i in dom A & j in Seg n holds
Deleting (block_diagonal (R ^ <*A*>),a),(i + (Sum (Len R))),(j + (Sum (Len R))) = block_diagonal (R ^ <*(Deleting A,i,j)*>),a

let a be Element of K; :: thesis: for R being FinSequence_of_Square-Matrix of K
for A being Matrix of n,K st i in dom A & j in Seg n holds
Deleting (block_diagonal (R ^ <*A*>),a),(i + (Sum (Len R))),(j + (Sum (Len R))) = block_diagonal (R ^ <*(Deleting A,i,j)*>),a

let R be FinSequence_of_Square-Matrix of K; :: thesis: for A being Matrix of n,K st i in dom A & j in Seg n holds
Deleting (block_diagonal (R ^ <*A*>),a),(i + (Sum (Len R))),(j + (Sum (Len R))) = block_diagonal (R ^ <*(Deleting A,i,j)*>),a

let A be Matrix of n,K; :: thesis: ( i in dom A & j in Seg n implies Deleting (block_diagonal (R ^ <*A*>),a),(i + (Sum (Len R))),(j + (Sum (Len R))) = block_diagonal (R ^ <*(Deleting A,i,j)*>),a )
assume A1: ( i in dom A & j in Seg n ) ; :: thesis: Deleting (block_diagonal (R ^ <*A*>),a),(i + (Sum (Len R))),(j + (Sum (Len R))) = block_diagonal (R ^ <*(Deleting A,i,j)*>),a
set b = block_diagonal R,a;
set B = <*(block_diagonal R,a)*>;
set AA = <*A*>;
set LRA = Sum (Len (R ^ <*A*>));
set LBA = Sum (Len (<*(block_diagonal R,a)*> ^ <*A*>));
set iS = i + (Sum (Len R));
set jS = j + (Sum (Len R));
A2: ( len A = n & width A = n ) by MATRIX_1:25;
then A3: ( n >= 1 & dom A = Seg n ) by A1, FINSEQ_1:4, FINSEQ_1:def 3, NAT_1:14;
A4: Len R = Width R by Th46;
A5: len (block_diagonal R,a) = Sum (Len R) by Def5;
A6: ( Len (R ^ <*A*>) = (Len R) ^ (Len <*A*>) & Len (<*(block_diagonal R,a)*> ^ <*A*>) = (Len <*(block_diagonal R,a)*>) ^ (Len <*A*>) & Len <*A*> = <*(len A)*> & Len <*(block_diagonal R,a)*> = <*(len (block_diagonal R,a))*> & Width (<*(block_diagonal R,a)*> ^ <*A*>) = (Width <*(block_diagonal R,a)*>) ^ (Width <*A*>) & Width <*A*> = <*(width A)*> & Width <*(block_diagonal R,a)*> = <*(width (block_diagonal R,a))*> & Len (<*(block_diagonal R,a)*> ^ <*A*>) = Width (<*(block_diagonal R,a)*> ^ <*A*>) ) by Th14, Th15, Th18, Th19, Th46;
then A7: ( Sum (Len (R ^ <*A*>)) = (len A) + (Sum (Len R)) & Sum (Len (<*(block_diagonal R,a)*> ^ <*A*>)) = (len A) + (Sum (Len <*(block_diagonal R,a)*>)) & Sum (Len (<*(block_diagonal R,a)*> ^ <*A*>)) = (Sum (Width <*A*>)) + (width (block_diagonal R,a)) & Sum (Len <*(block_diagonal R,a)*>) = len (block_diagonal R,a) & Sum (Len <*A*>) = len A & Sum (Width <*(block_diagonal R,a)*>) = width (block_diagonal R,a) ) by RVSUM_1:103, RVSUM_1:104, RVSUM_1:106;
per cases ( n = 1 or n > 1 ) by A3, XXREAL_0:1;
suppose A8: n = 1 ; :: thesis: Deleting (block_diagonal (R ^ <*A*>),a),(i + (Sum (Len R))),(j + (Sum (Len R))) = block_diagonal (R ^ <*(Deleting A,i,j)*>),a
then A9: ( i = 1 & j = 1 ) by A1, A3, FINSEQ_1:4, TARSKI:def 1;
len (Deleting A,i,j) = 1 -' 1 by A1, A8, LAPLACE:2
.= 0 by XREAL_1:234 ;
then A10: Deleting A,i,j = {} ;
thus Deleting (block_diagonal (R ^ <*A*>),a),(i + (Sum (Len R))),(j + (Sum (Len R))) = Deleting (block_diagonal (<*(block_diagonal R,a)*> ^ <*A*>),a),(i + (Sum (Len R))),(j + (Sum (Len R))) by A5, A7, Th35
.= Segm (block_diagonal (<*(block_diagonal R,a)*> ^ <*A*>),a),((Seg (Sum (Len (<*(block_diagonal R,a)*> ^ <*A*>)))) \ {(i + (Sum (Len R)))}),((Seg (Sum (Len (<*(block_diagonal R,a)*> ^ <*A*>)))) \ {(j + (Sum (Len R)))}) by MATRIX13:58
.= Segm (block_diagonal (<*(block_diagonal R,a)*> ^ <*A*>),a),(Seg (Sum (Len <*(block_diagonal R,a)*>))),((Seg (Sum (Len (<*(block_diagonal R,a)*> ^ <*A*>)))) \ {(j + (Sum (Len R)))}) by A2, A5, A7, A8, A9, FINSEQ_1:12
.= Segm (block_diagonal (<*(block_diagonal R,a)*> ^ <*A*>),a),(Seg (Sum (Len <*(block_diagonal R,a)*>))),(Seg (Sum (Width <*(block_diagonal R,a)*>))) by A2, A5, A6, A7, A8, A9, FINSEQ_1:12
.= block_diagonal R,a by Th32, A7
.= block_diagonal <*(block_diagonal R,a)*>,a by Th34
.= block_diagonal (<*(block_diagonal R,a)*> ^ <*(Deleting A,i,j)*>),a by A10, Th40
.= block_diagonal (R ^ <*(Deleting A,i,j)*>),a by Th35 ; :: thesis: verum
end;
suppose n > 1 ; :: thesis: Deleting (block_diagonal (R ^ <*A*>),a),(i + (Sum (Len R))),(j + (Sum (Len R))) = block_diagonal (R ^ <*(Deleting A,i,j)*>),a
then A11: width A = width (DelLine A,i) by A2, LAPLACE:4;
thus Deleting (block_diagonal (R ^ <*A*>),a),(i + (Sum (Len R))),(j + (Sum (Len R))) = DelCol (DelLine (block_diagonal (R ^ <*A*>),a),(i + (Sum (Len R)))),(j + (Sum (Len R))) by MATRIX_2:def 8
.= DelCol (block_diagonal (R ^ <*(DelLine A,i)*>),a),(j + (Sum (Len R))) by A1, A11, Th42
.= block_diagonal (R ^ <*(DelCol (DelLine A,i),j)*>),a by A4, A1, A2, A11, Th44
.= block_diagonal (R ^ <*(Deleting A,i,j)*>),a by MATRIX_2:def 8 ; :: thesis: verum
end;
end;