I guess most people who had a look into Parks paper from 1970 asked themself how Park defines least fixpoint.

At this point one does notice that he does not use the term fixpoint, rather he talks about convergence. When looking up the definition of convergence on wikipedia however, this will lead to filterconvergence (german link:

https://de.wikipedia.org/wiki/Filterkonvergenz) and the term Berührpunkte.

The question is:

Conv(c) = <Conv_0(c),Conv_0(c),\dots Conv_{N-1}(c)>

Conv_i(c) = \bigcap{A_i|c(<A>) \subseteq <A> for some {A_k|k\not = i}}

Are Conv_i as defined by Park therefore Berührpunkte?

This leads to some confusion regarding pre-fixpoints, since Park uses a union of conv_i as criterion for convergence, while we learned that the least fixpoints is the intersection (not the union) of all pre-fixpoints and therefore conv_i can not be the pre-fixpoint but something else. Thus convergenve should be identical to either least fixpoints or greatest fixpoints? Are there some indices missing in the definition of Conv and Conv_i?