Iteratively beta-reduces a top-level beta-redex on the right-hand side of an
equation.
DESCRIBE
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]
FAILURE
Fails unless the theorem is equational, with its right-hand side being
a top-level beta-redex.