  Mixing for measure-preserving group actions is a fundamental notion in
ergodic theory, with different phenomena arising for different acting groups.
In 1993, Klaus Schmidt and Tom Ward proved that 2-mixing implies mixing of all
orders for actions by commuting automorphisms of connected groups. Tom Ward
explains how he became interested in this problem, and describes how a chance
encounter with a paper on a seemingly unrelated problem in number theory played
a key role.
