let n be Nat; :: thesis: for M1, M2 being Matrix of n,REAL st M1 is Positive & M2 is Negative & |:M2:| is_less_than |:M1:| holds
M1 + M2 is Positive

let M1, M2 be Matrix of n,REAL; :: thesis: ( M1 is Positive & M2 is Negative & |:M2:| is_less_than |:M1:| implies M1 + M2 is Positive )
assume that
A1: M1 is Positive and
A2: M2 is Negative and
A3: |:M2:| is_less_than |:M1:| ; :: thesis: M1 + M2 is Positive
A4: Indices M2 = [:(Seg n),(Seg n):] by MATRIX_0:24;
A5: Indices (M1 + M2) = [:(Seg n),(Seg n):] by MATRIX_0:24;
A6: Indices M1 = [:(Seg n),(Seg n):] by MATRIX_0:24;
for i, j being Nat st [i,j] in Indices (M1 + M2) holds
(M1 + M2) * (i,j) > 0
proof
let i, j be Nat; :: thesis: ( [i,j] in Indices (M1 + M2) implies (M1 + M2) * (i,j) > 0 )
assume A7: [i,j] in Indices (M1 + M2) ; :: thesis: (M1 + M2) * (i,j) > 0
then [i,j] in Indices |:M2:| by A4, A5, Th5;
then |:M2:| * (i,j) < |:M1:| * (i,j) by A3;
then |.(M2 * (i,j)).| < |:M1:| * (i,j) by A4, A5, A7, Def7;
then |.(M2 * (i,j)).| < |.(M1 * (i,j)).| by A6, A5, A7, Def7;
then A8: |.(M1 * (i,j)).| - |.(M2 * (i,j)).| > 0 by XREAL_1:50;
M2 * (i,j) < 0 by A2, A4, A5, A7;
then A9: - (M2 * (i,j)) = |.(M2 * (i,j)).| by ABSVALUE:def 1;
M1 * (i,j) > 0 by A1, A6, A5, A7;
then M1 * (i,j) = |.(M1 * (i,j)).| by ABSVALUE:def 1;
then (M1 * (i,j)) + (M2 * (i,j)) > 0 by A9, A8;
hence (M1 + M2) * (i,j) > 0 by ; :: thesis: verum
end;
hence M1 + M2 is Positive ; :: thesis: verum