operator theory
mathematical study of linear operators on function spaces, such as differential operators and integral operators
en-US/ˈɑpəˌɹeɪdɚ ˌθiəˌɹi/
en-GB/ˈɒpəˌɹeɪtə θɪəɹiː/
mathematical study of linear operators on function spaces, such as differential operators and integral operators