[gtp] No I?

[Chris Spencer]

I suppose this may be explained somewhere, but I've been at a lose to 
discover it. Why do GTP coordinates not use the letter I? SGF uses I, or 
at least doesn't mention it explicitly 
(http://www.red-bean.com/sgf/go.html). Most non-GTP go board markups 
I've seen use I. Sensei's Library lists some answers to this question, 
but they seem fairly vague and inconclusive. Is there a real reason or 
is it just convention?

Chris