Cleanup pairs [Obj,Obj]

Description

Cleanup pairs in SOURCE, by e.g. removing self-pairs, symmetrical pairs, etc. When removing symmetrical pairs, it is unknown which of the two variants (a,b) or (b,a) will be removed.

Input

• SOURCE [OBJ,OBJ]: a list of object pairs

Output

• RESULT [OBJ,OBJ]: a list of object pairs