reserve s for set,
  i,j for natural Number,
  k for Nat,
  x,x1,x2,x3 for Real,
  r,r1,r2,r3,r4 for Real,
  F,F1,F2,F3 for real-valued FinSequence,
  R,R1,R2 for Element of i-tuples_on REAL;
reserve z,z1,z2 for Element of COMPLEX;
reserve n for Nat,
  x, y, a for Real,
  p, p1, p2, p3, q, q1, q2 for Element of n-tuples_on REAL;

theorem Th134:
  |(p1-p2, p3)| = |(p1, p3)| - |(p2, p3)|
proof
  |(p1 - p2, p3)| = |(p1, p3)| + |(-p2, p3)| by Th130
    .= |(p1, p3)| + - |(p2, p3)| by Th132;
  hence thesis;
end;
