[Combined Fragment:018]: Delete a Combined Fragment

It SHALL be possible to delete a combined fragment. All the fragments of all the interaction operands, will be deleted. Any message attached to an outer gate of the combined fragment and it is related fragments will be also removed.

The gaps left between the previous fragments and the combined fragment and between the previous fragments and the related deleted fragments will be closed by shifting up the elements along the lifelines that the interaction use occupied, an amount equivalent to the height of the gap.