reserve X for non empty UNITSTR;
reserve a, b for Real;
reserve x, y for Point of X;
reserve X for RealUnitarySpace;
reserve x, y, z, u, v for Point of X;
reserve seq, seq1, seq2, seq3 for sequence of X;
reserve  n for Nat;

theorem
  seq - x = seq + -x
proof
  let n be Element of NAT;
  thus (seq - x).n = seq.n - x by NORMSP_1:def 4
    .= (seq + -x).n by Def6;
end;
