let n be Nat; :: thesis: for R being Ring
for M1, M2 being Matrix of n,R st M1 commutes_with M2 holds
M1 * M2 commutes_with M2
let R be Ring; :: thesis: for M1, M2 being Matrix of n,R st M1 commutes_with M2 holds
M1 * M2 commutes_with M2
let M1, M2 be Matrix of n,R; :: thesis: ( M1 commutes_with M2 implies M1 * M2 commutes_with M2 )
A1: ( width M1 = n & width M2 = n ) by MATRIX_0:24;
A2: ( len M1 = n & len M2 = n ) by MATRIX_0:24;
assume M1 commutes_with M2 ; :: thesis: M1 * M2 commutes_with M2
then (M1 * M2) * M2 = M2 * (M1 * M2) by A1, A2, MATRIX_3:33;
hence M1 * M2 commutes_with M2 ; :: thesis: verum