Why does isabelle's preorder requires to provide less _and...
Isabelle's preorder class requires providing both less_eq and less: class ord = fixes less_eq :: "'a ⇒ 'a ⇒ bool" and less :: "'a ⇒ 'a ⇒ bool" class preorder = ord + assumes less_le_not_le: "x < y ⟷ x ≤ y ∧ ¬ (y ≤ x)" and order_refl ...