log:supports, log:implies, and conditional proof

Tim, Yosi,

The code for checking log:supports proof reminded me of conditional 
proof:

1. Show A->B
1a. A [assumption for conditional proof]
1b ...
1c. B

which makes me wonder: what's the difference between log:implies and 
log:supports?


-- 
Dan Connolly, W3C http://www.w3.org/People/Connolly/