The Vatican and U.S. Roman Catholic bishops are investigating the writings of a well-known American theologian who has analyzed how the Catholic faith relates to other religions. The inquiry's focus is the Rev. Peter Phan, of Georgetown University, a Vietnamese-American priest from the Dallas diocese and former president of the Catholic Theological Society of America. The U.S. bishops' Committee on Doctrine has traded correspondence with Phan since July 2005 seeking clarification on his writings, said Sister Mary Ann Walsh, a spokeswoman for the United States Conference of Catholic Bishops. "There was not complete satisfaction with his response, which is why...