Set-off for speculation losses: restricted to other speculation profits, with limited carryforward and priority over certain allowances. Losses from a speculation business may be set off solely against profits of other speculation businesses and, if not fully absorbed, carried forward to be set off only against future speculation profits within a limited number of succeeding tax years. Carryforward of related allowances is to be effected after applying these set off rules. For companies, purchase and sale of other companies' shares is deemed speculation business to the extent of that activity, subject to specified exclusions for entities with chiefly different income heads or whose principal business is share trading, banking, or lending.