User blog comment:Deedlit11/Ordinal Notations VI: Up to a weakly compact cardinal/@comment-5150073-20140515153351/@comment-1605058-20140521140851

From what I understand, D is diagonalizer of ordinal function F if F(D) is limit of 0,F(0),F(F(0)),F(F(F(0))),... or something like that.