let M1 be Matrix of n,K; :: thesis: ( M1 = a * M implies M1 is subsymmetric )
assume A1: M1 = a * M ; :: thesis: M1 is subsymmetric
A2: Indices M = [:(Seg n),(Seg n):] by MATRIX_0:24;
let i, j, k, l be Nat; :: according to MATRIX17:def 1 :: thesis: ( [i,j] in Indices M1 & k = (n + 1) - j & l = (n + 1) - i implies M1 * (i,j) = M1 * (k,l) )
assume that
A3: [i,j] in Indices M1 and
A4: ( k = (n + 1) - j & l = (n + 1) - i ) ; :: thesis: M1 * (i,j) = M1 * (k,l)
Indices M1 = [:(Seg n),(Seg n):] by MATRIX_0:24;
then ( k in Seg n & l in Seg n ) by A3, A4, Lm2;
then A5: [k,l] in [:(Seg n),(Seg n):] by ZFMISC_1:87;
A6: [i,j] in Indices M by A2, A3, MATRIX_0:24;
then (a * M) * (i,j) = a * (M * (i,j)) by MATRIX_3:def 5
.= a * (M * (k,l)) by A4, A6, Def1
.= (a * M) * (k,l) by A2, A5, MATRIX_3:def 5 ;
hence M1 * (i,j) = M1 * (k,l) by A1; :: thesis: verum