When applied to an equational theorem, RIGHT_LIST_BETA applies beta-reduction
over a top-level chain of beta-redexes to the right hand side (only). Variables
are renamed if necessary to avoid free variable capture.
A |- s = (\x1...xn. t) t1 ... tn
---------------------------------- RIGHT_LIST_BETA
A |- s = t[t1/x1]...[tn/xn]