GHCi, version 6.8.2: http://www.haskell.org/ghc/  :? for help
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Prelude> import Data.Graph.Inductive.Example
Prelude Data.Graph.Inductive.Example> star 6

<interactive>:1:0:
    Ambiguous type variable `gr' in the constraint:
      `Data.Graph.Inductive.Graph.Graph gr'
        arising from a use of `star' at <interactive>:1:0-5
    Probable fix: add a type signature that fixes these type variable(s)
Prelude Data.Graph.Inductive.Example> Leaving GHCi.