actualize
   list-del

with
   nat
by morphism
   :elem → nat; 
   :list → natlist; 
   [] → []; 
   .first → .head; 
   .rest → .tail; 
   + → mktwo; 
   -1l → -p; 
   + → +; 
   # → #; 
   ' → '; 
   + → +; 
   + → +; 
   ++ → ++; 
   rmdup → rmdup; 
   .last → .last; 
   .butlast → .butlast; 
   butlastn → butlastn; 
   rev → rev; 
   mklist → mklist; 
   fillfirst → fillfirst; 
   -l → -l; 
   -1l → -1l; 
   ] → ]; 
   pos → pos; 
   ] → ]; 
   sublist → sublist; 
   firstn → firstn; 
   restn → restn; 
   lastn → lastn; 
   frome → frome; 
   < → <; 
   ∈ → ∈; 
   dups → dups; 
   disj → disj; 
   ⊑ → ⊑; 
   ⊒ → ⊒; 
   a → n2; 
   b → n3; 
   c → n4; 
   a0 → n5; 
   x → X; 
   y → X0; 
   z → X1; 
   x0 → X2; 
   y0 → X3; 
   z0 → X4; 
   x1 → X5; 
   y1 → X6; 
   z1 → X7; 
   x2 → X8; 
   y2 → X9; 
   z2 → X10
end actualize