26 Their position, somewhat oversimplified, is as follows. HPPL and others including each of the Children executed, or are bound by, a deed described as the Hope Downs deed. Clause 7(b) is an undertaking by each of the parties to the deed not to challenge the right of any member of the Hancock Group, which means HPPL and any related body corporate of HPPL, to any of the Hancock Group interests which includes the Hancock Group's interest in the Hope Downs tenements and the Hope Downs joint venture. HPPL says that the applicants in the Federal Court Proceeding are precluded by the deed from pursuing its claims against HPPL in relation to the Hope Downs tenements and Hope Downs joint venture. The applicants submit that the deed does not preclude them from pursuing their claims and furthermore the deed should be set aside on grounds including misrepresentation, fraudulent concealment, misleading and deceptive conduct, unconscionable conduct, undue influence and duress. HPPL says that whether or not the applicants are precluded by cl 7(b) from pursuing the relevant claims should be referred to arbitration because the Hope Downs deed contains an arbitration clause. Justice Gleeson determined in effect that the arbitration clause prima facie covers the issue of whether the applicants may maintain the relevant claims and should be referred to arbitration if the arbitration agreement is valid and enforceable. The applicants maintain that the arbitration agreement, together with the rest of the Hope Downs deed, is null and void and unenforceable for the reasons for which they say the deed should be set aside. Her Honour has referred that question to a preliminary hearing - the proviso hearing. Justice Gleeson's decision to conduct the proviso hearing as a preliminary hearing is the subject of the appeal to the Full Federal Court. Mr Finch says that whatever the outcome of the appeal, there are various possible outcomes of the Federal Court Proceeding. If HPPL is successful in the proviso hearing, the right of the applicants to sue will be referred to arbitration. If HPPL is successful in its arguments before the arbitrator then the arbitrator will determine that the Children are bound by a covenant not to sue and that will preclude any further agitation of their claim in the Federal Court or this court and, Mr Finch says, it would make the joinder of the Children to these proceedings unnecessary. Further, Mr Finch says that if the Children have already been joined then the joinder will have to be unwound. It will be impossible to unwind some things such as the inspection of documents discovered by the other parties. If, on the other hand, HPPL is unsuccessful in its argument about the efficacy of the covenant not to sue then the Children will be entitled to maintain their claim to the relevant assets and at that point there will be a live claim in the Federal Court. Mr Finch says that at that time a determination would need to be made as to how and in what court the conflicting claims should be resolved. In summary, Mr Finch says that there are proceedings in the Federal Court, one outcome of which may be that the Children never get to sue in respect of the contested assets. If that is the case, this court should not exercise its discretion to join them on the basis that they are entitled to sue where there is no prejudice to any party to deferring the question of joinder until the Federal Court Proceeding, and possibly the arbitration, has determined whether the Children are entitled to sue and it is necessary to join them.