Merge several sorted collections into a single sorted collection. Each input collection must be sorted by the natural ordering of the type (it's implementation of IComparable<T>). The merging is stable; equal items maintain their ordering, and equal items in different collections are placed in the order of the collections.

Merge several sorted collections into a single sorted collection. Each input collection must be sorted by the ordering in the passed instance of IComparer<T>. The merging is stable; equal items maintain their ordering, and equal items in different collections are placed in the order of the collections.

Merge several sorted collections into a single sorted collection. Each input collection must be sorted by the ordering in the passed Comparison<T> delegate. The merging is stable; equal items maintain their ordering, and equal items in different collections are placed in the order of the collections.