theorem
  R1 = R1 + R - R
proof
  thus R1 = R1 + (i|->(0 qua Real)) by BINOP_2:2,FINSEQOP:56
    .= R1 + (R - R) by Th8,Th9,BINOP_2:2,FINSEQOP:73
    .= R1 + R - R by RFUNCT_1:23;
end;
