Some definitions of interest.
disjoint_sublists	Def disjoint_sublists(T;L1;L2;L) Def == f1:(||L1||||L||), f2:(||L2||||L||). Def == increasing(f1;||L1||) & (j:||L1||. L1[j] = L[(f1(j))]  T) Def == & increasing(f2;||L2||) & (j:||L2||. L2[j] = L[(f2(j))]  T) Def == & (j1:||L1||, j2:||L2||. f1(j1) = f2(j2))
	Thm* T:Type, L1,L2,L:T List. disjoint_sublists(T;L1;L2;L)  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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