Iv4aa = IMF Articles of Agreement (aa) - Article IV -Section 4
"The determination shall be made in light of the evolution of the international monetary system, with particular reference to sources of liquidity..."
Another interesting section Article III - Section 4. Substitution of securities for currency
"The Fund shall accept from any member, in place of any part of the member's currency in the General Resources Account which in the judgment of the Fund is not.....