Celebratio Mathematica

M. L. Cartwright: “Al­most peri­od­ic solu­tions of dif­fer­en­tial equa­tions and their ba­sic fre­quen­cies,” pp. 205–​207 in Pro­ceed­ings of the fifth in­ter­na­tion­al con­fer­ence on non-lin­ear os­cil­la­tions (Kiev, 25 Au­gust–4 Septem­ber 1969), Sec­tion 2: Qual­it­at­ive meth­ods in the the­ory of non­lin­ear os­cil­la­tions. Edi­ted by Y. Mitro­pol’skii. Izdat. Akad. Nauk Ukrain. S.S.R. (Kiev), 1970. Zbl 0229.​34042 incollection