let j, k, l, n, m, i be Nat; :: thesis: for K being non empty doubleLoopStr
for a being Element of K
for M, M1 being Matrix of n,m,K
for pK, qK being FinSequence of K st i in Seg n & j in Seg (width M) & k in dom M & pK = Line (M,l) & qK = Line (M,k) & M1 = RLine (M,l,((a * qK) + pK)) holds
( ( i = l implies M1 * (i,j) = (a * (M * (k,j))) + (M * (l,j)) ) & ( i <> l implies M1 * (i,j) = M * (i,j) ) )

let K be non empty doubleLoopStr ; :: thesis: for a being Element of K
for M, M1 being Matrix of n,m,K
for pK, qK being FinSequence of K st i in Seg n & j in Seg (width M) & k in dom M & pK = Line (M,l) & qK = Line (M,k) & M1 = RLine (M,l,((a * qK) + pK)) holds
( ( i = l implies M1 * (i,j) = (a * (M * (k,j))) + (M * (l,j)) ) & ( i <> l implies M1 * (i,j) = M * (i,j) ) )

let a be Element of K; :: thesis: for M, M1 being Matrix of n,m,K
for pK, qK being FinSequence of K st i in Seg n & j in Seg (width M) & k in dom M & pK = Line (M,l) & qK = Line (M,k) & M1 = RLine (M,l,((a * qK) + pK)) holds
( ( i = l implies M1 * (i,j) = (a * (M * (k,j))) + (M * (l,j)) ) & ( i <> l implies M1 * (i,j) = M * (i,j) ) )

let M, M1 be Matrix of n,m,K; :: thesis: for pK, qK being FinSequence of K st i in Seg n & j in Seg (width M) & k in dom M & pK = Line (M,l) & qK = Line (M,k) & M1 = RLine (M,l,((a * qK) + pK)) holds
( ( i = l implies M1 * (i,j) = (a * (M * (k,j))) + (M * (l,j)) ) & ( i <> l implies M1 * (i,j) = M * (i,j) ) )

let pK, qK be FinSequence of K; :: thesis: ( i in Seg n & j in Seg (width M) & k in dom M & pK = Line (M,l) & qK = Line (M,k) & M1 = RLine (M,l,((a * qK) + pK)) implies ( ( i = l implies M1 * (i,j) = (a * (M * (k,j))) + (M * (l,j)) ) & ( i <> l implies M1 * (i,j) = M * (i,j) ) ) )
assume that
A1: i in Seg n and
A2: j in Seg (width M) and
A3: k in dom M and
A4: pK = Line (M,l) and
A5: qK = Line (M,k) and
A6: M1 = RLine (M,l,((a * qK) + pK)) ; :: thesis: ( ( i = l implies M1 * (i,j) = (a * (M * (k,j))) + (M * (l,j)) ) & ( i <> l implies M1 * (i,j) = M * (i,j) ) )
thus ( i = l implies M1 * (i,j) = (a * (M * (k,j))) + (M * (l,j)) ) :: thesis: ( i <> l implies M1 * (i,j) = M * (i,j) )
proof
(a * (Line (M,k))) . j = a * (M * (k,j)) by A2, A3, Th3;
then consider a1 being Element of K such that
A7: a1 = (a * (Line (M,k))) . j ;
assume A8: i = l ; :: thesis: M1 * (i,j) = (a * (M * (k,j))) + (M * (l,j))
A9: (Line (M,l)) . j = M * (l,j) by A2, MATRIX_0:def 7;
then consider a2 being Element of K such that
A10: a2 = (Line (M,l)) . j ;
a * qK is Element of (width M) -tuples_on the carrier of K by A5, FINSEQ_2:113;
then (a * qK) + pK is Element of (width M) -tuples_on the carrier of K by A4, FINSEQ_2:120;
then A11: len ((a * qK) + pK) = width M by CARD_1:def 7;
then j in dom ((a * qK) + pK) by A2, FINSEQ_1:def 3;
then A12: ((a * qK) + pK) . j = the addF of K . (a1,a2) by A4, A5, A7, A10, FUNCOP_1:22
.= (a * (M * (k,j))) + (M * (l,j)) by A2, A3, A9, A7, A10, Th3 ;
width M1 = width M by A6, A11, MATRIX11:def 3;
then M1 * (i,j) = (Line (M1,i)) . j by A2, MATRIX_0:def 7
.= (a * (M * (k,j))) + (M * (l,j)) by A1, A6, A8, A11, A12, MATRIX11:28 ;
hence M1 * (i,j) = (a * (M * (k,j))) + (M * (l,j)) ; :: thesis: verum
end;
assume A13: i <> l ; :: thesis: M1 * (i,j) = M * (i,j)
a * qK is Element of (width M) -tuples_on the carrier of K by A5, FINSEQ_2:113;
then (a * qK) + pK is Element of (width M) -tuples_on the carrier of K by A4, FINSEQ_2:120;
then len ((a * qK) + pK) = width M by CARD_1:def 7;
then width M1 = width M by A6, MATRIX11:def 3;
hence M1 * (i,j) = (Line (M1,i)) . j by A2, MATRIX_0:def 7
.= (Line (M,i)) . j by A1, A6, A13, MATRIX11:28
.= M * (i,j) by A2, MATRIX_0:def 7 ;
:: thesis: verum