Q. A 58 year-old gentleman presents with a transient ischemic attack. He suffers from brief aphasia and right-side of body weakness. He is hospitalized for an evaluation for cardioembolic causes of TIA. On exam, you auscultate an irregularly irregular rhythm and EKG is performed, which confirms the presence of atrial fibrillation. You decide to start him on anticoagulation with warfarin. Which of the following is the mechanism of action for warfarin?