User blog comment:Wythagoras/Buchholz hydra/@comment-5029411-20130902145548

What if U for a Unfoldable and S for a Strong?

And for Ex-Extended Array Hydra:

Ex-Extended Array Rule 1: (...0(1) m+1n+1 ) = (...0( ...0(... ...0( ...0(1) m1(1)m+1n )m1(1)m+1n ...)m1(1)m+1n )m1(1)m+1n ).

Ex-Extended Array Rule 2: (...(@) 1... ) = (...(@)...)