:: VarDef = VarDef String [FieldSelector]
:: FieldSelector = FieldHd | FieldTl | FieldFst | FieldSnd
:: Op1 = UnNegation | UnMinus
:: VarDef = VarDef String [FieldSelector]
:: FieldSelector = FieldHd | FieldTl | FieldFst | FieldSnd
:: Op1 = UnNegation | UnMinus