alternativeChildren :: T.Tree (Feature a) -> [Feature a]
alternativeChildren ftree = concat [children f | f <- subtrees ftree, isAlternative (fnode f)]
alternativeChildren :: T.Tree (Feature a) -> [Feature a]
alternativeChildren ftree = concat [children f | f <- subtrees ftree, isAlternative (fnode f)]
alternativeChildren ftree = concat [children f | f <- subtrees ftree, isAlternative (fnode f)]