IBFD International Tax Glossary, 6th ed. Amsterdam: IBFD, 2009. P. 451.

United States Model Technical Explanation Accompanying The United States Model Income Tax Convention of November 15, 2006.

Convention between the Republic of Hungary and the Republic of Kazakhstan for the avoidance of Double Taxation and the Prevention of Fiscal Evasion with Respect to Taxes on Income and on Capital (effective of 1 January 1997); Convention between the Kingdom of the Netherlands and the Republic of Poland for the Avoidance of Double Taxation and the Prevention Of Fiscal Evasion with Respect to Taxes on Income (effective of 1 January 2004).