theorem
  R1 = R1 - R + R
proof
  thus R1 = R1 + (i|->(0.K)) by Lm2
    .= R1 + (-R + R) by Th26
    .= R1 + -R + R by FINSEQOP:28
    .= R1 - R + R by FINSEQOP:84;
end;
