... devoted to nonholonomic mechanics. In the paper ['Die Bewegungsleichungen konservativer Systeme mit linearen Bewegungsintegralen' Ⓣ (1910)], he considers the first integrals, which are linear with respect to velocities, as nonholonomic constraints. This idea permitted him to reduce a dynamical system with $n$ degrees of freedom to a system with fewer degrees of freedom. At the end of this analysis, using the energy integral, he eliminated time in the differential equations of motion. In another paper [published in 1914], he discovered a nonholonomic constraint and called this constraint a nonholonomic pendulum. In the same paper, he gave a method for construction of such a pendulum.

One part of the life of Academician Anton Bilimovic, the longer and more important one, belongs to Belgrade, the Serbian Academy of Sciences and Arts and Belgrade University. In Belgrade he started a new life of university professor and scientist in the new milieu. He was working in Belgrade with the same mental energy as in his motherland Russia. We see that Serbia arduously accepted him. He was highly respected in Serbia.

Professor Bilimovic published 138 scientific works, 22 scientific papers, 35 books and textbooks, many of them with several editions, 9 texts for popular use, 15 reviews and 15 reports. The main characteristic of his scientific opus is that he did not address only problems of one narrow scientific field, but Bilimovic also studied the problems of theory of curves and surface, rational mechanics, celestial mechanics and geophysics, nonanalytical functions and vector calculus. Especially in rational mechanics, he was occupied by phenomenological principles, motion of the rigid body around fixed point, dynamics of elastic bodies and equations of motion.

Pfaff's linear form or Pfaff's expression [are named] after Johann Friedrich Pfaff, who founded the theory of such differential forms. Pfaff's expression and Pfaff's equations are closely related to other mathematical concepts, which occupy an important place in modern mathematics. Applications of integral invariants were made by Henri Poincaré, Élie Cartan and George Birkhoff for the first time, and the relationships between the theory of integral invariants and Pfaff's expression underlines the importance. On the other hand, the so-called Pfaff method in mechanics was presented for the first time by Edmund Taylor Whittaker in 1904. The relation between Pfaff's expression and differential equations in canonical form was established by George Prange and Ernst Schering. In his preface Bilimovic first gives the phenomenological interpretation of a principle of mechanics which is called Pfaff's principle and the substance of which, in a different form, has been known for quite a long time. The applications of that principle have proved to be very convenient, its theory being, especially in recent time, evaluated very intensively. Then, he uses that principle for the formulation of a general phenomenological differential principle. The phenomenological derivation of that principle and the phenomenological interpretation of its procedure, i.e., its algorism, is the main purpose of this treatise.

He was a great example of how to become a good teacher and a good man. From his students he always required hard work and a deep understanding of the studied material. He did not like students whose hard work was consisting just of mental learning. He started and finished lessons exactly at a scheduled time. When once he was late for the lesson, he apologised and formulated the following theorem: "Even when professor is late, there always will be a student who arrives later". Just then one student entered the classroom. Professor Bilimovic said to students: "Now, the theorem is proved."