Questions from Dijkstra's EWD 1300: "The notational conventions I adopted, and why"
Conjunction and disjunction are dual, but if conjunction has higher precedence than disjunction, then dual to p ∧ q ∨ r is (p ∨ q) ∧ r != p ∨ q ∧ r.
As you can see exc is dif with its arguments flipped: exc(x, y) = y - x. min is probably short for "minus", not "minimum".