Def null(as) == Case of as; nil  true ; a.as'  false

is mentioned by

Thm* L:T List. L  nil  null(L)	[iseg_nil]
Thm* L1,L2:T List. null(L2)  L1  tl(L2)  L1  L2	[sublist_tl]
Thm* L:T List, x:T. null(L)  last([x / L]) = last(L)	[last_cons]
Thm* T:Type, L:T List. null(L)  last(L)  T	[last_wf]
Thm* L:T List, x:T. (x  L)  null(L)	[member_null]
Thm* L:T List, x:T. null(L)  (x  L)	[null_member]

In prior sections: list 1

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