Tax concession for foreign oil contractors: reduced taxation and blended calculation for mixed income under section 293A. Notification grants income-tax relief to foreign companies and non-resident persons engaged in mineral-oil prospecting or production: if total income consists only of such profits, tax is fifty per cent of that income; if total income is mixed, tax equals fifty per cent on mineral-oil profits plus tax on the remaining income at the average rate that would have applied to total income absent the concession; 'average rate of income-tax,' 'foreign company,' and 'mineral oil' are defined for these purposes.