Modal System K Modal System D 1.□(𝐴⊃𝐵)⊃(□𝐴⊃□𝐵) □(A⊃B)⊃(□A⊃□B) □(A→B)→(□A→□B)Modal Axiom Kaxiom▲ Modal System K 2.⊢𝜙□𝜙 <div>⊢𝜙</div><div class="den">□𝜙</div> <div>⊢𝜙</div><div class="den">□𝜙</div>Necessitation ruleaxiom▲ Modal System K