theorem
  a*mlt(R1,R2) = mlt(a*R1,R2) & a*mlt(R1,R2) = mlt(R1,a*R2)
proof
  thus a*mlt(R1,R2) = mlt(a*R1,R2) by FINSEQOP:26;
  thus a*mlt(R1,R2) = a*mlt(R2,R1) by FINSEQOP:33
    .= mlt(a*R2,R1) by FINSEQOP:26
    .= mlt(R1,a*R2) by FINSEQOP:33;
end;
