| Clefs allowed for this instrument.
allowedClefs      :: Instrument -> Set Clef
allowedClefs = Data.Set.fromList . Data._allowedClefs . fetchInstrumentDef

-
allowedClefs      :: Instrument -> Set Clef
allowedClefs = Data.Set.fromList . Data._allowedClefs . fetchInstrumentDef
allowedClefs = Data.Set.fromList . Data._allowedClefs . fetchInstrumentDef