BTree[Key; Val] = object
  root: Node[Key, Val]
  entries: int               ## number of key-value pairs
  

proc add[Key, Val](b: var BTree[Key, Val]; key: Key; val: Val)

proc contains[Key, Val](b: BTree[Key, Val]; key: Key): bool

proc getOrDefault[Key, Val](b: BTree[Key, Val]; key: Key): Val

proc hasNext[Key, Val](b: BTree[Key, Val]; index: int): bool

proc initBTree[Key, Val](): BTree[Key, Val]

proc len[Key, Val](b: BTree[Key, Val]): int {.inline.}

proc next[Key, Val](b: BTree[Key, Val]; index: int): (Key, Val, int)

iterator pairs[Key, Val](b: BTree[Key, Val]): (Key, Val)