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 FINSEQOP:28;
end;
