Congratulation from the researchers of the Software Laboratory of the Institute of Mathematics of the Siberian Branch of the USSR Ac. Sci. (With a hand-written Ershov's explanatory remark addressed to his mother.) Date: 20.04.1981 Original document language: Russian Organizations: Inst. of Mathematics of the Siberian Branch of the USSR Ac. Sci. Addressee: Andrei Petrovich Ershov
