The next meeting of the Algebra and Logic Seminar will be held on June 28, 2019 (Friday) at 1:00 p.m. in Room 578 of the Institute of Mathematics and Informatics. A talk on The approach of intersecting null four-dimensional gravitational cones and a new theory of GPS intersatellite communications between moving satellites in the (near-Earth) gravitational field will be delivered by Bogdan G. Dimitrov (Instutute of Nuclear Research and Nuclear Energy at BAS and Institute of Advanced Physical Studies, New Bulgarian University). Everybody is invited.