The tax law requires taxpayers to substantiate any deduction for expenses for entertainment, including meals, as well as for the business use of entertainment facilities by adequate records or other evidence corroborrating his own statement that establish the amount of the expense, as well as the time, place and business purpose of the expense or use, and the business relationship to the taxpayer of the person incurring the expense or using the facility or for whom the expense or use was incurred. To avoid disallowance of expenses, taxpayers are permitted to authenticate their expenditures by "adequate records or by sufficient evidence corroborating the taxpayer's own statement."