S. 115JA : Book profit-Mining, production and generation of aluminum, generated power-Captive power plant (CPP) for internal consumption-Profits derived from CPP was to be reduced from book profits-Provision for liability in respect of post-retirement medical benefits and leave encashment determined as an accrued liability and computed on basis of actuarial valuation by assessee could not be included in its book profits. [S. 115JA(iv)]