For instance, Lord NcNair does not believe that it is opposable by virtue of estoppel.

The Temple of Preah Vihar case shows the extremely close relationship between the various forms of State conduct estoppel, silence and acquiescence.

The Court considered the concept of estoppel, as can be seen from the passage from its decision transcribed below, even though it nowhere refers to the concept by name

It is interesting to note that in the reasoning of the Court the elements of estoppel and acquiescence are combined, as Judge Fitzmaurice points out in his separate opinion

Alternatively, as indicated above, payment of the pre dissolution arrears could be sought from the five successor States and the post dissolution balance could be sought from Serbia and Montenegro based on the principle of estoppel.

It is worth stressing another aspect that the Court noted, namely, that in this context the concepts of estoppel or acquiescence mingle with the general rule of recourse to the subsequent practice of the parties as a means of interpretation of a treaty.

See P. Cahier, Le comportement des Etats comme source de droits et d'obligations , Recueil d'études de droit international en homage à Paul Guggenheim (Geneva, 1968), pp. 248 249 and I. Sinclair, Estoppel and Acquiescence , Essays in Honour of Sir Robert Jennings (Cambridge, 1995), p. 110.

The conduct in question relates to categories of silence, acceptance, acquiescence and estoppel, all forms of unilateral conduct of States that undoubtedly produce legal effects similar to the effects of an act considered as an expression of will formulated with the intention of producing legal effects.

But acquiescence can operate as a preclusion or estoppel in certain cases, for instance where silence, on an occasion where there was a duty or need to speak or act, implies agreement, or a waiver of rights, and can be regarded as a representation to that effect

A third option would be for the Assembly to seek payment from the five successor States of arrears arising before the dissolution of the Socialist Federal Republic of Yugoslavia and to seek payment of the balance from Serbia and Montenegro based on the principle of estoppel, as outlined above.

The principle of preclusion is the nearest equivalent in the field of international law to the common law rule of estoppel, though perhaps not applied under such strict limiting conditions (and it is certainly applied as a rule of substance and not merely as one of evidence or procedure).

See, among others, R. Jennings, The Acquisition of Territory (Oxford, 1963), pp. 47 49 J. P. Cot, AFDI (1962), p. 244 E. Pecourt García, El principio de estoppel y la sentencia del Tribunal Internacional de Justicia en el caso del Templo de Preah Vihear , REDI, vol. 16 (1963), pp. 153 166.