S.S.Sandhawalia, J.

1. The complexities of the practical application of the otherwise settled principles of constructive res judicata have necessitated this reference to the Full Bench. The question for determination has been formulated in the following terms:-

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"Whether the decision of the High Court declining to issue a writ of mandamus on the assumption that a statutory rule was valid operates as res judicata in a subsequent suit instituted after the statutory rule had been declared as unconstitutional by the Supreme Court of India?"

The facts are not in dispute and a brief marshalling thereof with particular reference to the issue of law involved, therefore, suffices. Pt Nand Kishore, respondent, was employed a an Assistant in the Food Distribution Branch of the Punjab Civil Secretariat when he was compulsorily retired from service by an order in the following terms:-

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"Order of the Governor of Punjab: Sanction is accorded under the provisions of Rule 5.32(b) of the Punjab Civil Services Rules, Volume II, to the compulsory retirement from Government service of Shri Nand Kishore Assistant Food Distribution Branch, Punjab Civil Secretariat, with immediate effect. 2. He