Impermissible avoidance arrangement presumption: steps aimed at tax benefit trigger anti-avoidance scrutiny and rebuttable evidentiary burden. An impermissible avoidance arrangement is one primarily aimed at obtaining a tax benefit and is indicated where it creates non-arm's-length rights or obligations, results in misuse or abuse of the Act, lacks commercial substance (or is deemed to do so), or employs means not ordinarily used for bona fide purposes. A statutory presumption treats any step or part of an arrangement whose main purpose is to obtain a tax benefit as establishing that the arrangement was entered into for that purpose, unless the assessee disproves the presumption.