Timothy and Rostrum,
We all agree that the exchange is not equal. The fact that it is unequal might be the spur that drives the Green Man to balance the scales, in this case a search through time to some moment where Severian is as helplessly captive as the Green Man was. That is, the Green Man is very thankful and anxious to repay the favor--knowing full well that his utterance on Agia was inadequate.
I agree with Rostrum that Severian's gift is more out of mercy/compassion (all that stuff torturers aren't supposed to have; as such, an important developmental stage for Severian). If he had known that the Green Man was a genie, he might have tried bargining, or whatever--but all he saw was a hokey sideshow act that treated a man worse than an animal.
Re: the underground of worldship Yesod, more proof that Work Is Hell. <g>
=mantis=