**{1,1,2} and {1,2} are exactly the same set**, in other words, that :

             {1,1,2} =  {1,2} , or, if you prefer {1,2} = {1,1,2}

**{1,2} U Empty set.**

**"P OR Contradiction" is equivalent to P.**

{1,2} U Empty set = the set of all x such that x belongs  {1,2}.