question: public DoubleStreamEx prepend ( DoubleStream other ) { return new DoubleStreamEx ( DoubleStream . concat ( other , stream ( ) ) , context . combine ( other ) ) ; }
target:  Creates a lazily concatenated stream whose elements are all the elements of the other stream followed by all the elements of this stream. The resulting stream is ordered if both of the input streams are ordered, and parallel if either of the input streams is parallel. When the resulting stream is closed, the close handlers for both input streams are invoked.