1 A useful work on the UNIDROIT Principles and hardship as a concept might be had in Maskow, D., Hardship and Force Majeure  40 Am. J. Comp. L 657 (Mr Maskow, from Germany, was a member of the Working Group of UNIDROIT).
2See e.g. Berger, K.P., Renegotiation and Adaptation of International Investment Contracts: The Role of Contract Drafters and Arbitrators, 36 Vand. J. Transnat'l L 1347 (Oct. 2003); Gotanda, J., Renegociation and Adaptation Clauses in Investment Contracts, Revisited, ibid., at 1461; Nagla, N., Sanctity Of Contracts Revisited: A Study In Theory And Practice Of Long-Term International Commercial Transaction (Martinis Nijhoff 1995); Wolfgan, P., Arbitration and Renegociation of International Investment Agreements (Kluwer); Hillman, R.A., 'Court Adjustment of Long-Term Contracts: An Analysis under Modern Contract Law', 1987 Duke Law Journal 1; Clayton Gillette, 'Commercial Rationality and the Duty to Adjust Long-Term Contracts', 69 Minnesota Law Review 521 (Feb. 1985).
3Some perhaps seen to be stronger than others: Article 89(1) of the draft Common European Sales Law Regulation for example stresses that 'a party must perform its obligations even if performance has become more onerous, whether because the cost of performance has increased or because the value of what is to be received in return has diminished' whilst Article 6.2.1 of the UPICC might be seen as less exacting in its terms: 'Where the performance of a contract becomes more onerous for one of the parties, that party is nevertheless bound to perform its obligations subject to the following provisions on hardship.'