Por que compilar este código:

triples( [], _,_,_)->
  [];

triples( Self, X, Y, none )->
  [ Result || Result = { X, Y, _} <- Self ].

relatório:

./simple_graph.erl:63: Warning: variable 'X' is unused
./simple_graph.erl:63: Warning: variable 'Y' is unused
./simple_graph.erl:64: Warning: variable 'X' is unused
./simple_graph.erl:64: Warning: variable 'X' shadowed in generate
./simple_graph.erl:64: Warning: variable 'Y' is unused
./simple_graph.erl:64: Warning: variable 'Y' shadowed in generate

E retorne resultado errado: auto completo.