In mathematics, the Lyapunov time is the characteristic timescale on which a dynamical system is chaotic.
 It is named after the Russian mathematician Aleksandr Lyapunov.
 It is defined as the inverse of a system's largest Lyapunov exponent.
Aleksandr Mikhailovich Lyapunov (Russian: Алекса́ндр Миха́йлович Ляпуно́в , ] ; June 6 [O.S. May 25] 1857 – November 3, 1918) was a Russian mathematician, mechanician and physicist.
 His surname is sometimes romanized as Ljapunov, Liapunov, Liapounoff or Ljapunow.
 He was the son of astronomer Mikhail Lyapunov and the brother of pianist and composer Sergei Lyapunov.
The Lyapunov–Malkin theorem (named for Aleksandr Lyapunov and ) is a mathematical theorem detailing nonlinear stability of systems.
In stability theory and nonlinear control, Massera's lemma, named after José Luis Massera, deals with the construction of the Lyapunov function to prove the stability of a dynamical system.
 The lemma appears in as the first lemma in section 12, and in more general form in as lemma 2.
 In 2004, Massera's original lemma for single variable functions was extended to the multivariable case, and the resulting lemma was used to prove the stability of switched dynamical systems, where a common Lyapunov function describes the stability of multiple modes and switching signals.
Yuri Vladimirovich Matiyasevich, (Russian: Ю́рий Влади́мирович Матиясе́вич ; born March 2, 1947, in Leningrad) is a Russian mathematician and computer scientist.
 He is best known for his negative solution of Hilbert's tenth problem (Matiyasevich's theorem), which was presented in his doctoral thesis at LOMI (the Leningrad Department of the Steklov Institute of Mathematics).
In applied mathematics and dynamical system theory, Lyapunov vectors, named after Aleksandr Lyapunov, describe characteristic expanding and contracting directions of a dynamical system.
 They have been used in predictability analysis and as initial perturbations for ensemble forecasting in numerical weather prediction.
 In modern practice they are often replaced by bred vectors for this purpose.
In the theory of ordinary differential equations (ODEs), Lyapunov functions are scalar functions that may be used to prove the stability of an equilibrium of an ODE.
 Named after the Russian mathematician Aleksandr Mikhailovich Lyapunov, Lyapunov functions (also called the Lyapunov’s second method for stability) are important to stability theory of dynamical systems and control theory.
 A similar concept appears in the theory of general state space Markov chains, usually under the name Foster–Lyapunov functions.
Géraud Sénizergues (born 1957) is a French computer scientist at the University of Bordeaux.
 With Yuri Matiyasevich he obtained results about the Post correspondence problem.
 He won the 2002 Gödel Prize "for proving that equivalence of deterministic pushdown automata is decidable"
Lyapunov is a lunar crater named for Aleksandr Lyapunov that is located along the east-northeastern limb of the Moon, and is viewed from the side by observers on Earth.
 The eastern rim of this crater just falls into the section of the Moon called the far side, and visibility of this formation is affected by libration.
In mathematics, the Lyapunov–Schmidt reduction or Lyapunov–Schmidt construction is used to study solutions to nonlinear equations in the case when the implicit function theorem does not work.
 It permits the reduction of infinite-dimensional equations in Banach spaces to finite-dimensional equations.
 It is named after Aleksandr Lyapunov and Erhard Schmidt.

Question: What occupation do Aleksandr Lyapunov and Yuri Matiyasevich have in common?
Answer: Russian mathematician