The second, better guide to the 1981 tax act--because it examines virtually all the key provisions (unlike Arenson's The New York Times Guide to Making the New Tax Law Work for You, p. 1315, which focused on the wage-earner's situation). On the docket: the statute's implications for those who indulge in commodities trading and more conventional commitments; incentives for small businesses (many of advantage to individuals); the indexing system that takes effect in 1985; the pros and cons of real-estate shelters; and industrial revenue bonds--whose interest returns will be tax-exempt if municipal issuers use the proceeds for mass-transit programs. Plus: considerable offbeat intelligence (such as the ways in which commercial fishermen can avoid paying federal unemployment taxes). Most of tax attorney Post's attention is devoted, naturally, to major matters--including the rules permitting all workers to establish Individual Retirement Accounts and the doubling of deductible contributions that can be made to Keogh Plans by the self-employed. He also looks over the much-publicized ""marriage penalty""--finding (in some detail) that the fiscal state of union is essentially unchanged. With lots of practical tips, an authoritative, accessible, and inclusive tax advisory--quick off the mark though it is.