theorem Th18:
  1r(#)f = f
proof
A1: now
    let c be Element of M;
    assume c in dom (1r(#)f);
    hence (1r(#)f)/.c = 1r * f/.c by Def2
      .= f/.c by CLVECT_1:def 5;
  end;
  dom (1r(#)f) = dom f by Def2;
  hence thesis by A1,PARTFUN2:1;
end;
