SQL Server Query- How to Prune a table

I have a Table 'L2'

Itemset      Itemset2      
   1             3
   2             3
   2             5
   3             5

I created a [combination in pair of three] for these values in columns in table 'c3'

Itemset       Itemset2       itemset3
   1              3             5
   2              3             5
   1              2             3
   1              2             5

Like in Apriori I want to prune the table C3.

i.e. Getting this table as output 'C3Prune'

 Itemset       Itemset2       itemset3
   2              3             5

I want to create a SQL Server query for the same, I tried loops but it's not correct.

Please don't down vote the question if the question is not clear. I shall explain as many times needed in the comments. Thank you in advance.