let m, n be Nat; :: thesis: for K being Field
for M being Matrix of n,m,K
for i, j being Nat
for a being Element of K st M is without_repeated_line & j in dom M & ( i = j implies a <> - (1_ K) ) holds
Lin () = Lin (lines (RLine (M,i,((Line (M,i)) + (a * (Line (M,j)))))))

let K be Field; :: thesis: for M being Matrix of n,m,K
for i, j being Nat
for a being Element of K st M is without_repeated_line & j in dom M & ( i = j implies a <> - (1_ K) ) holds
Lin () = Lin (lines (RLine (M,i,((Line (M,i)) + (a * (Line (M,j)))))))

let M be Matrix of n,m,K; :: thesis: for i, j being Nat
for a being Element of K st M is without_repeated_line & j in dom M & ( i = j implies a <> - (1_ K) ) holds
Lin () = Lin (lines (RLine (M,i,((Line (M,i)) + (a * (Line (M,j)))))))

let i, j be Nat; :: thesis: for a being Element of K st M is without_repeated_line & j in dom M & ( i = j implies a <> - (1_ K) ) holds
Lin () = Lin (lines (RLine (M,i,((Line (M,i)) + (a * (Line (M,j)))))))

let a be Element of K; :: thesis: ( M is without_repeated_line & j in dom M & ( i = j implies a <> - (1_ K) ) implies Lin () = Lin (lines (RLine (M,i,((Line (M,i)) + (a * (Line (M,j))))))) )
assume that
A1: M is without_repeated_line and
A2: j in dom M and
A3: ( i = j implies a <> - (1_ K) ) ; :: thesis: Lin () = Lin (lines (RLine (M,i,((Line (M,i)) + (a * (Line (M,j)))))))
A4: len M = n by MATRIX_0:def 2;
set L = (Line (M,i)) + (a * (Line (M,j)));
A5: dom M = Seg (len M) by FINSEQ_1:def 3;
set R = RLine (M,i,((Line (M,i)) + (a * (Line (M,j)))));
per cases ( not i in dom M or i in dom M ) ;
suppose not i in dom M ; :: thesis: Lin () = Lin (lines (RLine (M,i,((Line (M,i)) + (a * (Line (M,j)))))))
hence Lin () = Lin (lines (RLine (M,i,((Line (M,i)) + (a * (Line (M,j))))))) by ; :: thesis: verum
end;
suppose A6: i in dom M ; :: thesis: Lin () = Lin (lines (RLine (M,i,((Line (M,i)) + (a * (Line (M,j)))))))
then n <> 0 by A5, A4;
then A7: width M = m by MATRIX_0:23;
then reconsider Li = Line (M,i), Lj = Line (M,j) as Vector of () by MATRIX13:102;
a * Lj = a * (Line (M,j)) by ;
then A8: (Line (M,i)) + (a * (Line (M,j))) = Li + (a * Lj) by ;
A9: ( not Li = Lj or a <> - (1_ K) or Li = 0. () )
proof
assume A10: Li = Lj ; :: thesis: ( a <> - (1_ K) or Li = 0. () )
( Li = M . i & Lj = M . j ) by ;
hence ( a <> - (1_ K) or Li = 0. () ) by ; :: thesis: verum
end;
reconsider L9 = (Line (M,i)) + (a * (Line (M,j))) as Element of the carrier of K * by FINSEQ_1:def 11;
reconsider LL = L9 as set ;
set iL = {i} --> L9;
len ((Line (M,i)) + (a * (Line (M,j)))) = width M by CARD_1:def 7;
then A11: RLine (M,i,((Line (M,i)) + (a * (Line (M,j))))) = M +* (i,LL) by MATRIX11:29
.= M +* (i .--> LL) by
.= M +* ({i} --> L9) by FUNCOP_1:def 9 ;
M .: ((dom M) \ (dom ({i} --> L9))) = (M .: (dom M)) \ (M .: (dom ({i} --> L9))) by
.= (rng M) \ (M .: (dom ({i} --> L9))) by RELAT_1:113
.= (rng M) \ (Im (M,i))
.= (rng M) \ {(M . i)} by
.= (rng M) \ {(Line (M,i))} by ;
then A12: lines (RLine (M,i,((Line (M,i)) + (a * (Line (M,j)))))) = (() \ {(Line (M,i))}) \/ (rng ({i} --> L9)) by
.= (() \ {(Line (M,i))}) \/ {((Line (M,i)) + (a * (Line (M,j))))} by FUNCOP_1:8 ;
A13: Lj in lines M by ;
Li in lines M by ;
hence Lin () = Lin (lines (RLine (M,i,((Line (M,i)) + (a * (Line (M,j))))))) by A8, A12, A13, A9, Th14; :: thesis: verum
end;
end;