I am writing an introduction and I want to know who introduced the concept of topological mixing?



Who introduced the concept of topological mixing?
Topological mixing is called "permanent regional transitivity" (and demonstrated) by Gustav Hedlund in his 1939 [article](http://projecteuclid.org/euclid.bams/1183501760) on the dynamics of the geodesic flow in constant negative curvature (third page). I think this is the first occurrence of the concept. 


