Print unique columns based on field matching 1

[dironman62]

I have this file where lines 1 and 3 match but in reversed fields, same for lines 2 and 4.

U1 U2
U2 U3
U2 U1
U3 U2
U3 U4

Want to print out lines that don't match, regardless of field, like this.

U1 U2
U2 U3
U3 U4

 

[CaKiwi]

I made a few assumptions about what you wanted, but this might get you started

!f1[$1,$2] && !f1[$2,$1] { f1[$1,$2]=1; print}

CaKiwi