# Transactions of the American Mathematical Society

Published by the American Mathematical Society since 1900, Transactions of the American Mathematical Society is devoted to longer research articles in all areas of pure and applied mathematics.

ISSN 1088-6850 (online) ISSN 0002-9947 (print)

The 2020 MCQ for Transactions of the American Mathematical Society is 1.48 .

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## $C^{2}$-preserving strongly continuous Markovian semigroupsHTML articles powered by AMS MathViewer

by W. M. Priestley
Trans. Amer. Math. Soc. 180 (1973), 359-365 Request permission

## Abstract:

Let $X$ be a compact ${C^2}$-manifold. Let $||\;||,||\;||β$ denote the supremum norm and the ${C^2}$-norm, respectively, and let $\{ {P^t}\}$ be a Markovian semigroup on $C(X)$. The semigroupβs infinitesimal generator $A$, with domain $\mathcal {D}$, is defined by $Af = {\lim _{t \to 0}}{t^{ - 1}}({P^t}f - f)$, whenever the limit exists in $||\;||$. Theorem. Assume that $\{ {P^t}\}$ preserves ${C^2}$-functions and that the restriction of $\{ {P^t}\}$ to ${C^2}(X),||\;||β$ is strongly continuous. Then ${C^2}(X) \subset \mathcal {D}$ and $A$ is a bounded operator from ${C^2}(X),||\;||β$ to $C(X),||\;||$. From the conclusion is obtained a representation of $Af \cdot (x)$ as an integrodifferential operator on ${C^2}(X)$. The representation reduces to that obtained by Hunt [Semi-groups of measures on Lie groups, Trans. Amer. Math. Soc. 81 (1956), 264-293] in case $X$ is a Lie group and ${P^t}$ commutes with translations. Actually, a stronger result is proved having the above theorem among its corollaries.
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