[Comment to Article 10.2.1.1: While it is theoretically possible for a Rider  or other Person to establish that the anti -doping rule violation was not intentional without showing how the Prohibited Substance entered one’s system, it is highly unlikely that in a doping case under Article  2.1 a Rider  will be successful in proving that the Rider  acted unintentionally without establishing the source of the Prohibited Substance.]