TITLE: Who introduced the concept of topological mixing?
QUESTION [7 upvotes]: I am writing an introduction and I want to know who introduced the concept of topological mixing?

REPLY [11 votes]: Topological mixing is called "permanent regional transitivity" (and demonstrated) by Gustav Hedlund in his 1939 article on the dynamics of the geodesic flow in constant negative curvature (third page). I think this is the first occurrence of the concept.