let n be Nat; :: thesis: for M1, M2 being Matrix of n, REAL holds |:(M1 + M2):| is_less_or_equal_with |:M1:| + |:M2:|
let M1, M2 be Matrix of n, REAL ; :: thesis: |:(M1 + M2):| is_less_or_equal_with |:M1:| + |:M2:|
A1: Indices M1 = [:(Seg n),(Seg n):] by MATRIX_1:25;
A2: Indices (M1 + M2) = [:(Seg n),(Seg n):] by MATRIX_1:25;
A3: Indices M2 = [:(Seg n),(Seg n):] by MATRIX_1:25;
for i, j being Nat st [i,j] in Indices |:(M1 + M2):| holds
|:(M1 + M2):| * i,j <= (|:M1:| + |:M2:|) * i,j

proof

let i, j be Nat; :: thesis: ( [i,j] in Indices |:(M1 + M2):| implies |:(M1 + M2):| * i,j <= (|:M1:| + |:M2:|) * i,j )
assume [i,j] in Indices |:(M1 + M2):| ; :: thesis: |:(M1 + M2):| * i,j <= (|:M1:| + |:M2:|) * i,j
then A4: [i,j] in Indices (M1 + M2) by Th5;
then [i,j] in Indices |:M1:| by A1, A2, Th5;
then A5: (|:M1:| + |:M2:|) * i,j = (|:M1:| * i,j) + (|:M2:| * i,j) by MATRIXR1:25
.= (abs (M1 * i,j)) + (|:M2:| * i,j) by A1, A2, A4, Def7
.= (abs (M1 * i,j)) + (abs (M2 * i,j)) by A3, A2, A4, Def7 ;
|:(M1 + M2):| * i,j = abs ((M1 + M2) * i,j) by A4, Def7
.= abs ((M1 * i,j) + (M2 * i,j)) by A1, A2, A4, MATRIXR1:25 ;
hence |:(M1 + M2):| * i,j <= (|:M1:| + |:M2:|) * i,j by A5, COMPLEX1:142; :: thesis: verum

end;

hence |:(M1 + M2):| is_less_or_equal_with |:M1:| + |:M2:| by Def6; :: thesis: verum