The interior purpose is closing around the free variable and that's why it known as 'closure'. A no cost variable is a variable that is outside the interior purpose and passed in to the inner via docorator. 1 Also see this identical problem and its solutions. Is apparently very similar, https://propertyingurugram.in/mantri-plan-to-link-2-key-junctions-with-elevated-road-gets-cm-manohar-lal-khattars-nod/