NOBEL LAUREATE P. A. M. Dirac, Lucasian professor of mathematics at Cambridge University, is reported to have been denied permission to enter the United States. Dirac, who has been in this country several times in recent years, was invited to come to Princeton this year as a visiting physicist at the Institute for Advanced Study, which is directed by J. R. Oppenheimer. On May 26th Dirac said that his visa application had been “turned down flat” under the terms of Section 212 A of the Immigration and Naturalization Act, a lengthy list of reasons for denying entry that covers categories of undesirables ranging from vagrants to stowaways.