code: func (it *Unique) Contains(ctx context.Context, val graph.Value) bool {
  	graph.ContainsLogIn(it, val)
  	it.runstats.Contains += 1
  	return graph.ContainsLogOut(it, val, it.subIt.Contains(ctx, val))
  }
docs: // Contains checks whether the passed value is part of the primary iterator,
  // which is irrelevant for uniqueness.