Permanent establishment: fixed place and agency rules determine taxable presence under the DTAA, with exclusions for auxiliary activities. The DTAA defines permanent establishment by reference to a fixed place of business and enumerated examples, and converts certain prolonged activities-construction projects, sustained service provision through personnel, and offshore resource operations-into permanent establishments based on duration thresholds. Exclusions cover premises used solely for storage, display, occasional delivery, stock maintenance for processing, purchasing, information collection, and other preparatory or auxiliary activities. Agency rules treat enterprises as having a permanent establishment when a person habitually concludes contracts, maintains delivery stock, or secures orders, while independent agents acting in their ordinary course are excluded.