theorem elList1 (A: set) (a: nat): $ a : 0 e. List A <-> a e. A $;
    
      
        | Step | Hyp | Ref | Expression | 
        
          | 1 | 
           | 
          bitr | 
          (a : 0 e. List A <-> a e. A /\ 0 e. List A) -> (a e. A /\ 0 e. List A <-> a e. A) -> (a : 0 e. List A <-> a e. A)  | 
        
        
          | 2 | 
           | 
          elListS | 
          a : 0 e. List A <-> a e. A /\ 0 e. List A  | 
        
        
          | 3 | 
          1, 2 | 
          ax_mp | 
          (a e. A /\ 0 e. List A <-> a e. A) -> (a : 0 e. List A <-> a e. A)  | 
        
        
          | 4 | 
           | 
          bian2 | 
          0 e. List A -> (a e. A /\ 0 e. List A <-> a e. A)  | 
        
        
          | 5 | 
           | 
          elList0 | 
          0 e. List A  | 
        
        
          | 6 | 
          4, 5 | 
          ax_mp | 
          a e. A /\ 0 e. List A <-> a e. A  | 
        
        
          | 7 | 
          3, 6 | 
          ax_mp | 
          a : 0 e. List A <-> a e. A  | 
        
      
    
    Axiom use
    axs_prop_calc
     (ax_1,
      ax_2,
      ax_3,
      ax_mp,
      itru),
    
axs_pred_calc
     (ax_gen,
      ax_4,
      ax_5,
      ax_6,
      ax_7,
      ax_10,
      ax_11,
      ax_12),
    
axs_set
     (elab,
      ax_8),
    
axs_the
     (theid,
      the0),
    
axs_peano
     (peano1,
      peano2,
      peano5,
      addeq,
      muleq,
      add0,
      addS,
      mul0,
      mulS)