446. Average base period net income-depressed industry sub-groups. 447. Industry base period rates of return. 448. Excess profits credit-regulated public utilities. 449. Personal service corporations. 450. Corporations engaged in mining of strategic minerals. 451. Capitalization of advertising, etc., expenditures. 452. Adjustment in case of position inconsistent with prior income tax liability. 453. Nontaxable income from certain mining and timber operations and from natural gas properties. 454. Exempt corporations. 455. Relief for installment basis taxpayers and taxpayers with income from long-term contracts. 456. Abnormalities in income in taxable period. |