Some definitions of interest.
iff	Def P  Q == (P  Q) & (P  Q)
	Thm* A,B:Prop. (A  B)  Prop
sublist	Def L1  L2 Def == f:(||L1||||L2||).  Def == increasing(f;||L1||) & (j:||L1||. L1[j] = L2[(f(j))]  T)
	Thm* T:Type, L1,L2:T List. L1  L2  Prop

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