T:Type, a,a':T, b,b':(T List). (cons(a; b) = cons(a'; b'))  guard(((a = a')  (b = b'))) 

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Definitions	prop{i:l}, t  T, P  Q, P  Q, P  Q, guard(T), P  Q, x:A. B(x), T, ff, tt, if b then t else f fi , True, False, A, A  B, ge(i; j), Unit, , Y, hd(l), ||as||, tl(l),
Lemmas	assert of le int, bnot of lt int, true wf, squash wf, eqff to assert, assert of lt int, eqtt to assert, iff transitivity, non neg length, ifthenelse wf, bnot wf, le wf, le int wf, hd wf, assert wf, bool wf, length wf1, lt int wf, tl wf