UNFOLD_RIGHT_RULE : (thm list -> thm -> thm)
A |- !z1 ... zr. t = ?y1 ... yp. t1 /\ ... /\ tn
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B u A |- !z1 ... zr. t = ?y1 ... yp. t1' /\ ... /\ tn'
#UNFOLD_RIGHT_RULE [ASSUME "!in out. INV(in,out) = !(t:num). out t = ~(in t)"]
# (ASSUME "!(in:num->bool) out. BUF(in,out) = ?l. INV(in,l) /\ INV(l,out)");;
.. |- !in out.
BUF(in,out) = (?l. (!t. l t = ~in t) /\ (!t. out t = ~l t))