paragraph: In 1917, Einstein applied the general theory of relativity to model the structure of the universe as a whole. He apprehended that his equations predicted the universe to be either contracting or expanding. He wanted the universe to be eternal and unchanging, but this type of universe is not consistent with relativity. To fix this, Einstein modified the general theory by introducing a new notion, the cosmological constant, which he called ''Lambda''. The purpose of Lambda was to rectify the effects of gravity and allow the whole system to stay balanced. With a positive cosmological constant, the universe could be an eternal static sphere. However, in 1929, Edwin Hubble confirmed that the universe is expanding, Einstein exclaimed after his Mount Wilson visit with Hubble: "If there is no quasi-static world, then away with the cosmological term!" and Einstein supposedly discarded the cosmological constant. Einstein believed a spherical static universe is philosophically preferred, because it would obey Mach's principle. He had shown that general relativity incorporates Mach's principle to a certain extent in frame dragging by gravitomagnetic fields, but he knew that Mach's idea would not work if space goes on forever. In a closed universe, he believed that Mach's principle would hold. Mach's principle has generated much controversy over the years. In many of Einstein biographies, writers claim that he called the creation of Lambda his "biggest blunder". Recently, astrophysicist Mario Livio showed that Einstein possibly never said that. Instead of discarding Lambda, Einstein was continually experimenting with it. In late 2013, Irish physicist Cormac O'Raifeartaigh, happened to discover a handwritten manuscript by Einstein which was since then overlooked by other scientists. The research paper was titled ''"Zum kosmologischen Problem"'' ("About the Cosmological Problem"). And Einstein proposed a revision of his model, still with a cosmological constant, but now the constant was responsible for the creation of new matter as the universe expanded. 
question: The discovery of an expanding universe by what scientist caused Einstein to discard his cosmological constant?
answer: Cormac O'Raifeartaigh