506Jurisdiction — Consent — ICSID Convention, Article 25 — Multi-party proceedings — Interpretation — Whether multi-party proceedings were compatible with the ICSID system and the BIT — Whether original submission of a multi-party proceeding required an act of consent on the part of the respondent beyond the general jurisdictional requirement of written consent — Whether the number of claimants affected the scope of the respondent’s consent to arbitration — Whether contractually unrelated persons could bring a claim together — Whether the number of claimants would prevent the tribunal from conducting the proceedings in accordance with the principles of fairness and due processJurisdiction — Consent — ICSID Convention, Article 25 — ICSID Convention, Article 36 — Due authorisation — Power of attorney — Whether the request for arbitration should have been signed by the claimants themselves — Whether the power of attorney in favour of counsel was validly executed — Whether the power of attorney empowered counsel to file the request for arbitration on behalf of the claimantsJurisdiction — Nationality — ICSID Convention, Article 25 — ICSID Convention, Article 43 — Burden of proof — Whether the burden of proof fell on the respondent to disprove that the claimants were not Italian nationals — Whether the evidentiary burden was satisfied through the identity documents submitted by the claimantsJurisdiction — Standing — Portfolio investment — Sovereign bonds — Domestic litigation — Whether the claimants lacked locus standi because of their remote connection with the underlying bonds — Whether certain claims brought before domestic courts against the issuers of security entitlement deprived the claimants of their locus standi in international arbitrationJurisdiction — Investment — Portfolio investment — Sovereign bonds — Territorial requirement — Interpretation — Whether security entitlements related to sovereign bonds were investments covered by the BITJurisdiction — Investment — Portfolio investment — Sovereign bonds — ICSID Convention, Article 25 — Interpretation — VCLT, Article 31 — Ordinary meaning — VCLT, Article 32 — Supplementary means — Whether the tribunal must interpret the meaning of investment in accordance with its ordinary meaning — Whether the tribunal must interpret the meaning of investment using supplementary meansJurisdiction — Investment — ICSID Convention, Article 25 — Salini test — Whether the four elements of the Salini test expressed mandatory jurisdictional requirements — Whether security entitlements issued in respect of sovereign bonds met the Salini test507 Jurisdiction — Sovereign acts — Whether the impugned measures were sovereign acts constituting prima facie breaches of the BITJurisdiction — Domestic litigation requirement — Consultation — Effective redress — Whether the provisions under the BIT laid down mandatory jurisdictional requirements — Whether the duty to consult was satisfied by the claimants — Whether the claimants violated the requirement to have recourse to the domestic courts prior to their request for international arbitration