reserve N for Nat;
reserve n,m,n1,n2 for Nat;
reserve q,r,r1,r2 for Real;
reserve x,y for set;
reserve w,w1,w2,g,g1,g2 for Point of TOP-REAL N;
reserve seq,seq1,seq2,seq3,seq9 for Real_Sequence of N;

theorem Th27:
  |.w1 - w2.| = |.w2 - w1.|
proof
  thus |.w1 - w2.| = |.-(w1 - w2).| by EUCLID:71
    .= |.w2 - w1.| by RLVECT_1:33;
end;
