Thames-Dick (P) entered into a master agreement with the Puerto Rico Aqueduct and Sewer Authority (PRASA) to construct, operate, and maintain the North Coast Superaqueduct Project (the Project). P granted subcontracts for various portions of the work. One such contractor was D. After completion, a segment of the pipeline burst. P incurred significant costs in repairing the damage. Litigation ballooned and spilled over into federal court. A googol of claims, counterclaims, cross-claims, and third-party complaints followed. Some of these were brought against D. To complicate matters, one of the defendants moved to dismiss on grounds that, inter alia, (1) CPA had failed to join an indispensable party whose presence would destroy diversity jurisdiction, and (2) the existence of the parallel proceeding in the local court counseled in favor of abstention. While this motion was pending before the district court, P asked that the case be referred to mediation and suggested Professor Eric Green as a suitable mediator. D objected, but the court ordered non-binding mediation to proceed before Professor Green. The court directed all parties to undertake mediation in good faith; stayed discovery pending completion of the mediation; and declared that participation in the mediation would not prejudice the parties' positions vis-a-vis the pending motion or the litigation as a whole. The court also stated that if mediation failed to produce a global settlement, the case would proceed to trial. D sought reconsideration, and when that was denied, D sought relief by mandamus. D alleged that the district court did not have the authority to require mediation (especially in light of unresolved questions as to the court's subject-matter jurisdiction) and, in all events, could not force D to pay a share of the expenses of the mediation.