Hi John, there are a couple of typos in the proof:
"To prove that sometimes", the meet is used rather than the join.
The same error in the line above the QED.
My stab at Puzzle 22 starting from the definition that \( \lnot X = X \to \bot \) in a
Heyting Algebra. This requires that we have a bounded lattice with a smallest and greatest element.
This definition \( \lnot X = X \to \bot \) means that \( X …
Regarding the question as to the simplest DAG that's not a Hasse Diagram (#96), what about the graph with \(V = \{x, y\}, E = \{\{x, y\}, \{x, y\}\}\)? i.e. two vertices and two edges going in the same direction connecting them?
It's a valid DAG bu…