Truth isn’t Truth

#! /usr/bin/haskell
import Data.List
statementList :: [String]
statementList =
  ["What I tell you three times is true."
  ,"Truth isn’t truth."
  ,"Truth isn’t truth."
  ,"1+1=2."
  ,"Truth isn’t truth."
  ,"What I tell you three times is true."
  ,"What I tell you three times is true."
  ]
atLeastThrice :: [String] -> [String]
atLeastThrice sL =
  [head grp | grp <-
    group $ sort sL, length grp >= 3]

 
Result (if loaded and executed in GHCi):

*Main> atLeastThrice statementList
["Truth isn’t truth.","What I tell you three times is true."]

 
(“1+1=2.” has not been proven true as it appears only once in the statement list.)