The binding legal principles established are: (1) Section 12A of the Competition Act mandates a strict two-stage analysis - first, whether the merger is likely to substantially lessen or prevent competition (using factors in s 12A(2)); second, whether it can be justified on public interest grounds (using factors in s 12A(3)). Public interest considerations cannot be considered at the first stage. (2) The Competition Tribunal must base its decisions on evidence before it and cannot engage in unjustified speculation, though predictive judgments based on evidence are required. (3) Proper market definition is essential to assessing competitive effects and must be conducted using recognized economic principles examining product substitutability and functional equivalence from a consumer perspective. (4) On appeal, while the Competition Appeal Court recognizes the Tribunal's specialist expertise in evaluating economic evidence and policy considerations, it will not defer to incorrect interpretations of statutory provisions or misapplication of legal tests. (5) A finding that a merger will substantially lessen competition must be justified by rigorous analysis of the evidence regarding market structure, competitors, barriers to entry, and competitive dynamics.