Serbia: 150 years since the birth of Kosta Stojanović

I receive a registered cover from Serbia with 3 stamps with Serbian scientist Kosta Stojanović.  He was a Serbian scientist in the fields of math, physics, mechanics, sociology and economy. He was pioneer in math economy and cybernetics in Serbia. He was professor at Belgrade Higher School and in The University of Belgrade. He was minister of economy 8 times in The Kingdom of Serbia and The Kingdom of Serbs, Croats and Slovenes. Date of issue is 10.04.2017.