It was submitted to Princeton later that year and he was awarded his Ph.D. Results from his dissertation appeared in the book Stability theory of differential equations which he published in 1953.
Ito ay isinumite sa Princeton sa susunod na taon at siya ay iginawad sa kanyang Ph.D. Mga resulta mula sa kanyang disertasyon ay lumitaw sa libro sa katatagan teorya ng kaugalian equation na kung saan siya nai-publish sa 1953.