AC*SE, you said, "If back to back tickets are against the airline's tariff, then it is illegal." TRUE, HOWEVER there is a difference between LEGAL nested tickets (which do not violate the tariff) and "back to back" tickets. I think you are confusing them. Basically, "back to back" tickets are from city A to city B and back. The two tickets are stripped and used to beat the saturday night stay. Nested tickets would look like this. Start in city A fly to B (THEN PRIOR TO RETURNING to A) fly to city C. Return to B. THEN, and only then, return to A. The key is you did not return home (to A) until the other flights were taken. All segments paid for were flown on the original days. None discarded, changed, or altered... NO violation. Hope this helps.