Playwright Itamar Moses discusses his new play, “Completeness,” about a computer scientist who hooks up with a molecular biologist. He's joined by actor Karl Miller, who plays the character Elliott, who builds a computer program to help Molly with her research project, the variables in their evolving relationship shift as rapidly as the terms of their experiment. “Completeness” is playing at Playwrights Horizons Mainstage Theater through September 25.