List: implement BidirectionalCollection; add specializations for first and last properties.
List: implement BidirectionalCollection; add specializations for first and last properties.

lorentey/BTree,Maaimusic/BTree,lorentey/BTree,Maaimusic/BTree,Maaimusic/BTree,eonil/BTree,lorentey/BTree,eonil/BTree,eonil/BTree