Codd's reduction algorithm

Hello, friends.

Could you help me in finding details
on Codd's reduction algorithm
and probably of its further developments
(e.g. for object-relational models, if any)?

Actually, I am interested in a (rigorous) proof
of equivalence of calculus and algebra
rather than in an algorithm per se.

Web resources are preferred.

Thanks.

-- 
Alexander E. Gutman
[EMAIL PROTECTED]