Surprisingly little judicial attention has been devoted to the concept of an “integer” of a claim, as that phrase was coined in Htun. That may explain why in 2013 Robertson J in SZRKT took the view that the authorities illuminated no clear distinction between “claims” on the one hand and “mere” items of evidence on the other. The phrase “integer” seems to have been used interchangeably with “component of claim” (Htun) yet in Tran v Minister for Immigration and Multicultural and Indigenous Affairs (Kiefel, RD Nicholson and Downes JJ) the opportunity for exposition was not taken up as the Full Court of the Federal Court of Australia merely stated that the tribunal was “required to deal with all integers of an applicant’s claim”, without providing elucidation about what an integer was. His Honour Judge Manousaridis has held that an “integer” may be taken to be the equivalent of a material question of fact. His Honour so held in SZURJ v Minister for Immigration and Border Protection that an integer was a meaningful subset of material questions of fact, which, in combination with other meaningful subsets of material questions of fact, ought to lead the Tribunal to conclude in a particular way. In my respectful view, his Honour’s consideration of the subject is accurate. It appears to be one of the only statements of principle on point. The sheer volume of decided migration cases in the federal jurisdiction over the last 10 years has overtaken observations in learned writings of the early millennium of which an example is Caron Beaton-Wells, ‘Judicial Review of Migration Decisions: Life After S157’. So far as my research has uncovered, the consideration given to the subject of integers by his Honour Judge Manousaridis is the best and only treatment on the point.
See Craig v The State of South Australia (1995) 184 CLR 163 esp at 179-180:
[T]he ordinary jurisdiction of a court of law encompasses authority to decide questions of law, as well as questions of fact, involved in matters which it has jurisdiction to determine. The identification of relevant issues, the formulation of relevant questions and the determination of what is and what is not relevant evidence are all routine steps in the discharge of that ordinary jurisdiction. Demonstrable mistake in the identification of such issues or the formulation of such questions will commonly involve error of law which may, if an appeal is available and is pursued, be corrected by an appellate court and, depending on the circumstances, found an order setting aside the order or decision of the inferior court. Such a mistake on the part of an inferior court entrusted with authority to identify, formulate and determine such issues and questions will not, however, ordinarily constitute jurisdictional error. Similarly, a failure by an inferior court to take into account some matter which it was, as a matter of law, required to take into account in determining a question within jurisdiction or reliance by such a court upon some irrelevant matter upon which it was, as a matter of law, not entitled to rely in determining such a question will not ordinarily involve jurisdictional error.
See also discussion in SZVDC v Minister for Immigration and Border Protection  FCAFC 16 in the context of applications under s 39B of the Judiciary Act in relation to a Federal Circuit Court judge’s refusal to extend time under s 477 of the Migration Act.
See the discussion about proportionality and the exercise of particular kinds of power, by Barker J in his speech http://www.fedcourt.gov.au/digital-law-library/judges-speeches/justice-barker/barker-j-20140725.
The test and authorities discussing factual permutations are discussed by Kenny J in VFAB v Minister for Immigration & Multicultural & Indigenous Affairs  FCA 872.
It is whether a fair-minded lay observer might reasonably apprehend that the Tribunal member might not have brought an impartial mind to the resolution of the question to be decided.
A particularly outrageous example is found in S233 of 2002  FMCA 39. See for example:
 It is also noteworthy that on that same page, at about point nine, that the turn that emerges from the text of the Tribunal members’ questioning of the applicant is, to say the least unfortunate, bearing on the sarcastic and I quote:
How can they possibly distribute these dissident leaflets in parks and cafes? How can that possibly happen? Do they walk around to people having picnics and say ‘will you please read this’? Do they interrupt someone in the middle of bowl of pho and say ‘Oh excuse me, just while you are having your pho would you please read this pamphlet’.
See obiter remarks entitled ‘Disturbing undercurrents’ by Flick J in Minister for Immigration and Citizenship v SZQRB  FCAFC 33.
See also - for a discussion about how personal non-compellable powers which may be exercised in the ‘public interest’ must still take into account relevant factors. It is an error to make a decision ‘irrespective of’ relevant factors: 
See the discussion in Plaintiff S297/2013 v Minister for Immigration and Border Protection (2015) 255 CLR 231 at  onwards.
If a denial of procedural fairness has deprived the applicant of a fair hearing, there is no need for the applicant to prove anything more. This is contrasted with the situation where a denial of procedural fairness did not otherwise result in a fair hearing (probably a rare situation).
See discussion in Minister for Immigration and Border Protection v WZARH  HCA 40; 256 CLR 326: per Gaegler and Gordon JJ at -:
The concern of procedural fairness, which here operates as a condition of the exercise of a statutory power, is with procedures rather than with outcomes. It follows that a failure on the part of an assessor or reviewer to give the opportunity to be heard which a reasonable assessor or reviewer ought fairly to give in the totality of the circumstances constitutes, without more, a denial of procedural fairness in breach of the implied condition which governs the exercise of the Minister’s statutory powers of consideration.
Such a breach of the implied condition which governs the exercise of the Minister’s statutory powers of consideration is material, so as to justify the grant of declaratory relief by a court of competent jurisdiction, if it operates to deprive the offshore entry person of “the possibility of a successful outcome”.
That approach to the determination of the existence and consequence of a breach of an implied condition of procedural fairness governing the exercise of a statutory power is wholly consistent with the often-repeated observation of Gleeson CJ in Re Minister for Immigration and Multicultural and Indigenous Affairs; Ex parte Lam that the concern of procedural fairness is to “avoid practical injustice”, and with his Honour’s conclusion in that case that there was no denial of procedural fairness where “[n]o practical injustice ha[d] been shown”. The absence of practical injustice in Lam lay in the fact that “[t]he applicant lost no opportunity to advance his case”; it was not “shown that he lost an opportunity to put any information or argument to the decision-maker, or otherwise suffered any detriment”.
Contrary to the submission of the Minister in this appeal, and as has repeatedly been recognised in the Full Court of the Federal Court, Lam is not authority for the proposition that it is incumbent on a person who seeks to establish denial of procedural fairness always to demonstrate what would have occurred if procedural fairness had been observed. What must be shown by a person seeking to establish a denial of procedural fairness will depend upon the precise defect alleged to have occurred in the decision-making process.
There are cases in which conduct on the part of an administrator in the course of a hearing can be demonstrated to have misled a person into refraining from taking up an opportunity to be heard that was available to that person in accordance with an applicable procedure which was otherwise fair. To demonstrate that the person would have taken some step if that conduct had not occurred is, in such a case, part of establishing that the person has in fact been denied a reasonable opportunity to be heard.
Where, however, the procedure adopted by an administrator can be shown itself to have failed to afford a fair opportunity to be heard, a denial of procedural fairness is established by nothing more than that failure, and the granting of curial relief is justified unless it can be shown that the failure did not deprive the person of the possibility of a successful outcome. The practical injustice in such a case lies in the denial of an opportunity which in fairness ought to have been given.
In Minister for Immigration and Multicultural and Indigenous Affairs v SCAR  FCAFC 126, the Court observed:
 On the other hand, it is also clear that s 425 of the Act imposes an objective requirement on the Tribunal. The statutory obligation upon the Tribunal to provide a “real and meaningful” invitation exists whether or not the Tribunal is aware of the actual circumstances which would defeat that obligation. Circumstances where it has been held that the obligations imposed by s 425 of the Act have been breached include circumstances where an invitation was given but the applicant was unable to attend because of ill health: Applicant NAHF of 2002 v Minister for Immigration and Multicultural and Indigenous Affairs  FCA 140. They also include circumstances where the statements made by the Tribunal prior to the hearing have misled the applicant as to the issues likely to arise before the Tribunal: VBAB of 2002 v Minister for Immigration and Multicultural and Indigenous Affairs  FCA 804. They also include circumstances where the fact or event resulting in unfairness was not realised by the Tribunal. For example, circumstances such as where the applicant was invited to attend and did attend before the Tribunal, but was effectively precluded from taking part because he could not speak English and a translator was not provided or was inadequate: Tobasi v Minister for Immigration and Multicultural Affairs  FCA 1050; W284 v Minister for Immigration and Multicultural Affairs  FCA 1788.
See also SZQBN v Minister for Immigration and Border Protection  FCA 686; 226 FCR 68 at  per Flick J and Gill v Minister for Immigration and Border Protection  FCAFC 51 at  per Griffiths and Moshinsky J.
The Minister’s common retort that making findings as to credibility is a task of the tribunal ‘par excellence’ is often abused. That tautology does not mean that credibility findings cannot be challenged in judicial review. Criticism of the abuse of ‘par excellence’ was made in CQG15 v Minister for Immigration and Border Protection  FCAFC 146 at -:
Before considering the arguments in detail, there is one topic which this appeal usefully highlights. That credibility is a matter par excellence for the Tribunal is an expression often used. It stems from Minister for Immigration and Multicultural Affairs; Ex parte Durairajasingham  HCA 1; 74 ALJR 405 per McHugh J. At - his Honour, sitting in the High Court’s original jurisdiction as a single judge, said (footnotes omitted):
67 In addition, the prosecutor alleges that the Tribunal breached s 430(1) by failing to set out reasons for its finding that the prosecutor’s claim that members of PLOTE tried to recruit him were “utterly implausible”. However, this was essentially a finding as to whether the prosecutor should be believed in his claim – a finding on credibility which is the function of the primary decision maker par excellence. If the primary decision maker has stated that he or she does not believe a particular witness, no detailed reasons need to be given as to why that particular witness was not believed. The Tribunal must give the reasons for its decision, not the sub-set of reasons why it accepted or rejected individual pieces of evidence. In any event, the reason for the disbelief is apparent in this case from the use of the word “implausible”. The disbelief arose from the Tribunal’s view that it was inherently unlikely that the events had occurred as alleged.
68 But there is a more fundamental reason why the argument based on s 430 fails to support a claim for prerogative relief. Even if, contrary to my view, there was a breach of s 430(1) by the Tribunal, it would not amount to a jurisdictional error. In Minister for Immigration and Ethnic Affairs v Eshetu, Gummow J referred to the requirement that, before granting a protection visa, the Minister and, on review, the Tribunal be “satisfied” that the prosecutor was a refugee. That requirement arose from ss 36 and 65 of the Act. His Honour said:
“A determination that the decision-maker is not ‘satisfied’ that an applicant answers a statutory criterion which must be met before the decision-maker is empowered or obliged to confer a statutory privilege or immunity goes to the jurisdiction of the decision-maker and is reviewable under s 75(v) of the Constitution.”
The prosecutor argued at the hearing that s 430(1)(c) “feeds into the ascertainment of the Minister’s satisfaction” and that it is “an integral part of ascertaining the jurisdictional fact”.
It is important to note that McHugh J’s observations and his Honour’s use of the phrase “par excellence” were made in the specific context of a claim that the Tribunal had not complied with its statutory obligation under s 430 of the Migration Act to give reasons for its decision. Nothing said by McHugh J suggests that the Tribunal’s adverse findings on credibility are not amenable to judicial review on jurisdictional error grounds. There is a risk that a mechanical use of the phrase “par excellence” as a formula fails sufficiently to appreciate this important reality. The fact that credibility is a matter for the Tribunal to determine as a question of fact does not mean that challenges to credibility are not open. This appeal illustrates three of a number of potential bases of challenge to credibility findings on well‑established legal precedent. In the present appeal, the foundation for the challenge is on the basis of no logical or probative basis for the finding in relation to ground 1, illogicality and/or irrationality in relation to ground 2, and, in relation to ground 3, a lack of natural justice.
There are several other potential bases upon which credit findings can be challenged. Recitation of the expression that credibility is a matter par excellence should not be understood as precluding challenges to credibility or, indeed, other findings of fact on any basis. While there is no suggestion in this case that this is what has occurred, the frequency of adoption of the expression should not obscure the availability of challenges on recognised grounds, such as:
(a) failure to afford procedural fairness;
(b) reaching a finding without any logical or probative basis;
(c) unreasonableness; and/or
(d) jurisdictional error as discussed by Flick J in SZVAP.
This term is used loosely. It was discussed by McHugh J in Ousley v R (1997) 192 CLR 69, page 99:
A collateral attack on an act or decision occurs when the act or decision is challenged in proceedings whose primary object is not the setting aside or modification of that act or decision. In In re Preston, however, Lord Scarman used the term “collateral challenge” to include any process challenging a decision – including an application for judicial review – other than a proceeding by way of appeal. This use of the term is readily intelligible. However, with the widespread availability of judicial review procedures, it conduces to clarity of thought, in my opinion, if the term “collateral challenge” is confined to challenges that occur in proceedings where the validity of the administrative act is merely an incident in determining other issues.
The Supreme Court of Victoria is a superior court of record. Judicial orders of superior courts cannot be made the subject of a collateral challenge. Such orders are valid until they are set aside or varied by appeal to a higher court even if they have been made in excess of jurisdiction. They cannot be treated as nullities. It is not open to an inferior court to ignore them. Indeed, a superior court “which, after a real trial, has given a valid decision determinative of right, liability or status, has no jurisdiction to recall it whatever mistakes may have been made in facts or law”. If warrants issued under the Act by the Supreme Court are judicial orders, it follows that the trial judge was correct in holding that he had no jurisdiction to entertain a collateral challenge to their validity.
These comments were adopted in Singh v Minister for Immigration  FCCA 387,  where Manousaridis J observed:
 … The expression “collateral attack” is often used to denote the challenging of an administrative act or delegated legislation “in proceedings where the validity of the administrative act [or delegated legislation] is merely an incident in determining other issues”.12 An example is Guo v Minister for Immigration and Citizenship where Besanko J considered whether a regulation made under s 504 of the Act was invalid.13 His Honour noted that the Minister did not suggest that a collateral attack on the validity of the regulation was not permissible, and that the appeal was conducted on the footing that if his Honour were to decide that the regulation in question was invalid, constitutional writs directed to the Tribunal should issue.14
Collateral challenges may nonetheless be permissible–the observations in Ousley are in relation to decisions made by a superior Court of record. Decision made by a Tribunal or officer of the Commonwealth or a State are different. Thus, in Robinson v Vanston  VSC 541, , Ashley JA observed:
Focussing, then, on the matter of principle, the making of a decision upon an application for classification is an administrative act. Prima facie it should be open to challenge by administrative law process. That should not prevent it being subject to collateral challenge, as to which see Ousley v The Queen (1997) 192 CLR 69 at 98- 99 per McHugh J.
More recently, in R v Debono  VSC 350; 222 A Crim R 194 Kyriou J observed at :
Administrative acts and decisions are generally susceptible to collateral challenge in a court. For example, a collateral challenge to the validity of a telecommunications interception warrant can be brought in the course of a trial, provided that the trial judge has jurisdiction to determine such a challenge. However, the scope of permissible collateral challenge is unclear.
Sometimes statute may limit the ability to mount a collateral attack. In Director of Housing v Sudi  VSCA 266; 33 VR 559 the Victorian Court of Appeal considered a situation where the Director made an application to VCAT for eviction orders under the Residential Tenancies Act. VCAT considered an argument that the anterior decision by the Director to make such an application at all was unlawful because of the Charter of Human Rights and Responsibilities. Maxwell P considered the issue from  onwards and concluded that the particular statutory scheme did not allow VCAT to uphold such a collateral attack.