reserve x,y,z for Real,
  x3,y3 for Real,
  p for Point of TOP-REAL 3;
reserve p1,p2,p3,p4 for Point of TOP-REAL 3,
  x1,x2,y1,y2,z1,z2 for Real;

theorem Th10:
  -p = |[ -p`1, -p`2, -p`3]|
proof
  thus -p = (-1)*p by RLVECT_1:16
    .= |[ (-1)*p`1, (-1)*p`2, (-1)*p`3]| by Th7
    .= |[ -p`1, -p`2, -p`3]|;
end;
