let a be Element of REAL ; :: thesis: for n being Nat
for M being Matrix of n, REAL st a < 0 & M is Negative holds
a * M is Positive
let n be Nat; :: thesis: for M being Matrix of n, REAL st a < 0 & M is Negative holds
a * M is Positive
let M be Matrix of n, REAL ; :: thesis: ( a < 0 & M is Negative implies a * M is Positive )
assume that
A1: a < 0 and
A2: M is Negative ; :: thesis: a * M is Positive
A3: Indices (a * M) = Indices M by MATRIXR1:28;
for i, j being Nat st [i,j] in Indices (a * M) holds
(a * M) * i,j > 0

proof

let i, j be Nat; :: thesis: ( [i,j] in Indices (a * M) implies (a * M) * i,j > 0 )
assume A4: [i,j] in Indices (a * M) ; :: thesis: (a * M) * i,j > 0
then M * i,j < 0 by A2, A3, Def2;
then a * (M * i,j) > 0 by A1, XREAL_1:132;
hence (a * M) * i,j > 0 by A3, A4, Th4; :: thesis: verum

end;

hence a * M is Positive by Def1; :: thesis: verum