“The cases indicate that as a matter of principle, first, proceedings in which the same issues or questions fall in substance to be determined should not be permitted to proceed in parallel. Secondly, in principle proceedings in one court should not be determined if there is a realistic 20 prospect that the matter decided would be moot, because the issue would become immaterial as a consequence of a decision of another court. Finally, those principles are founded upon the interests of justice, which will therefore fall to be applied in any case where the question whether to adjourn or stay is not determined as a matter of 25 principle.”