ws1s; ex2 X: all2 X1, X2, X3:( (X1 sub X2 & X2 sub X3) => X1 sub X3) & ( (X1 sub X3 & X3 sub X2) => X1 sub X2) & ( (X2 sub X1 & X1 sub X3) => X2 sub X3) & ( (X2 sub X3 & X3 sub X1) => X2 sub X1) & ( (X3 sub X1 & X1 sub X2) => X3 sub X2) & ( (X3 sub X2 & X2 sub X1) => X3 sub X1) & X1 sub X & X2 sub X & X3 sub X;