Even your party 2 ul to party 3 scenario its still not a trade.

I'll give you this gold medallion for that silver medallion - Thats a trade.

I'll give you this 5 dollar bill for that 5 dollar bill, how is that a trade? The seeder NEVER gets anything in return. Its still sharing all the way around. Even the 100th seeder doesnt get anything in return. Its still that same show being shared. In essence its just gift giving, but its not trading. The original seeder is under no obligation to seed anything and seeder 2 receives that gift but is not obligated to pass it on. Its all sharing, the word trade doesnt apply in any instance unless the individuals have a deal to seed this, and Ill seed that.

Torrents are not trades.