reserve v,x,x1,x2,y,z for object,
  X,X1,X2,X3 for set;

theorem
  for E,F,G be add-associative right_zeroed
      right_complementable non empty addLoopStr,
  x1 be Point of E, x2 be Point of F, x3 be Point of G
  holds -[x1,x2,x3] = [-x1,-x2,-x3]
proof
  let E,F,G be add-associative right_zeroed
  right_complementable non empty addLoopStr,
    x1 be Point of E, x2 be Point of F, x3 be Point of G;
  thus -[x1,x2,x3] = [-[x1,x2],-x3] by PRVECT_3:8
         .= [-x1,-x2,-x3] by PRVECT_3:8;
end;
