"I don't think Post often came to Princeton during the '30s. I can't remember ever seeing him in Princeton"

This quote by Stephen Cole Kleene recommends that the specific he is describing, Post, did not often check out Princeton during the 1930s. Kleene is indicating that he does not remember ever seeing Post in Princeton during that time period. This might indicate that Post did not check out Princeton throughout the 1930s, or that Kleene just did not have the opportunity to see him during that time. It is possible that Post did check out Princeton during the 1930s, however Kleene was not aware of it. It is also possible that Post did not check out Princeton throughout the 1930s, and Kleene's absence of memory of seeing him is an indicator of this. In either case, this quote implies that Post did rarely go to Princeton throughout the 1930s.