While I think everything written in this post is correct, what really is starting bothering me is this over-focus/attention on data even when what you want to express is behavior, let me explain:

The post talks about "transition invariants" that should be somehow different from "state invariants" yet it describe them as:

> These are predicates over a <<state, next-state>> pair ...

i.e. it still is about state, but I find it much more useful to focus on behavior so instead of thinking about how state transition you focus on what the program is allowed to perform, regardless of the underlying data structure.

What I mean is that I'd like the code to tell me why a certain piece can't do such move instead of why it cannot transition it's position to another position and basically dumping its state in my head and there I have to execute the program myself.