There is another account (which contradicts the foregoing) that in 1921 (or 1922 according to some) Keijiro NAKANISHI who was a student of the Waseda University Senior High School and others invented the sauce katsudon which then spread to restaurants around the School.
また、1921年（1922年説もあり）に早稲田高等学院生の中西敬二郎らがソースかつ丼を考案し周辺の店に広まった、との説もある（これは前説とは対立する）。