let i, j, n 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 that
A1: i in dom A and
A2: 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)
n <> 0 by A2;
then A3: n >= 1 by NAT_1:14;
set jS = j + (Sum (Len R));
set iS = i + (Sum (Len R));
set AA = <*A*>;
set b = block_diagonal (R,a);
set B = <*(block_diagonal (R,a))*>;
set LRA = Sum (Len (R ^ <*A*>));
set LBA = Sum (Len (<*(block_diagonal (R,a))*> ^ <*A*>));
A4: width A = n by MATRIX_0:24;
A5: Len R = Width R by Th46;
A6: len A = n by MATRIX_0:24;
then A7: dom A = Seg n by FINSEQ_1:def 3;
A8: Width <*A*> = <*(width A)*> by Th19;
A9: len (block_diagonal (R,a)) = Sum (Len R) by Def5;
A10: Len (<*(block_diagonal (R,a))*> ^ <*A*>) = Width (<*(block_diagonal (R,a))*> ^ <*A*>) by Th46;
A11: Len <*A*> = <*(len A)*> by Th15;
then A12: Sum (Len <*A*>) = len A by RVSUM_1:73;
Len (<*(block_diagonal (R,a))*> ^ <*A*>) = (Len <*(block_diagonal (R,a))*>) ^ (Len <*A*>) by Th14;
then A13: Sum (Len (<*(block_diagonal (R,a))*> ^ <*A*>)) = (len A) + (Sum (Len <*(block_diagonal (R,a))*>)) by A11, RVSUM_1:74;
A14: Width <*(block_diagonal (R,a))*> = <*(width (block_diagonal (R,a)))*> by Th19;
then A15: Sum (Width <*(block_diagonal (R,a))*>) = width (block_diagonal (R,a)) by RVSUM_1:73;
Width (<*(block_diagonal (R,a))*> ^ <*A*>) = (Width <*(block_diagonal (R,a))*>) ^ (Width <*A*>) by Th18;
then A16: Sum (Len (<*(block_diagonal (R,a))*> ^ <*A*>)) = (Sum (Width <*A*>)) + (width (block_diagonal (R,a))) by A14, A10, RVSUM_1:76;
Len <*(block_diagonal (R,a))*> = <*(len (block_diagonal (R,a)))*> by Th15;
then A17: Sum (Len <*(block_diagonal (R,a))*>) = len (block_diagonal (R,a)) by RVSUM_1:73;
per cases ( n = 1 or n > 1 ) by A3, XXREAL_0:1;
suppose A18: 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 A19: i = 1 by A1, A7, FINSEQ_1:2, TARSKI:def 1;
A20: j = 1 by A2, A18, FINSEQ_1:2, TARSKI:def 1;
len (Deleting (A,i,j)) = 1 -' 1 by A1, A18, LAPLACE:2
.= 0 by XREAL_1:232 ;
then A21: 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 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 A6, A9, A13, A17, A18, A19, FINSEQ_1:10
.= Segm ((block_diagonal ((<*(block_diagonal (R,a))*> ^ <*A*>),a)),(Seg (Sum (Len <*(block_diagonal (R,a))*>))),(Seg (Sum (Width <*(block_diagonal (R,a))*>)))) by A6, A4, A9, A11, A8, A13, A16, A17, A12, A15, A18, A20, FINSEQ_1:10
.= block_diagonal (R,a) by A17, A15, Th32
.= block_diagonal (<*(block_diagonal (R,a))*>,a) by Th34
.= block_diagonal ((<*(block_diagonal (R,a))*> ^ <*(Deleting (A,i,j))*>),a) by A21, 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 A22: width A = width (DelLine (A,i)) by A6, 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))))
.= DelCol ((block_diagonal ((R ^ <*(DelLine (A,i))*>),a)),(j + (Sum (Len R)))) by A1, A22, Th42
.= block_diagonal ((R ^ <*(DelCol ((DelLine (A,i)),j))*>),a) by A2, A4, A5, A22, Th44
.= block_diagonal ((R ^ <*(Deleting (A,i,j))*>),a) ; :: thesis: verum
end;
end;