Collection[T] = Sized and Container[T] and Iterable[T]

Container[T] = concept self
    T
    contains(self, T) is bool

Iterable[T] = concept self
    T
    when SupportIteratorHit:
      iterator items(self): T
    else:
      when defined(js):
        typeof(self.items(), ItemTypeMode) is T
      else:
        for value in self:
          value is T

Iterator[T] = concept selfof Iterable[T]
    T
    self.next is T

Mapping[K; V] = concept selfof Collection[K]
    K
    V
    self[K] is V

MutableSequence[T] = concept selfof Sequence[T]
    T
    self[int] = T
    self.delitem(int)
    self.insert(int, T)      ## insert item before index

Sequence[T] = concept selfof Collection[T]
    T
    self[int] is T

Sized = concept self
    len(self) is int