[Haskell-cafe] Tuple

HI Cafe I have to make a function to check that I have one occurrence of the last element (z) of the same list [a,b] in the tuple [([a,b],z)] For example [([1,2],3),([1,1],5),([1,3],6).......] this is true because there is one single z for each single list. while this one is false [([1,2],3),([1,2],5),([1,3],6).......] because 3&5 were found for the same list [1,2] any Idea how to code this Fn. Thanks