theorem b1lt (a b: nat): $ a < b <-> b1 a < b1 b $;
    
      
        | Step | Hyp | Ref | Expression | 
        
          | 1 | 
           | 
          bitr | 
          (a < b <-> b0 a < b0 b) -> (b0 a < b0 b <-> b1 a < b1 b) -> (a < b <-> b1 a < b1 b)  | 
        
        
          | 2 | 
           | 
          b0lt | 
          a < b <-> b0 a < b0 b  | 
        
        
          | 3 | 
          1, 2 | 
          ax_mp | 
          (b0 a < b0 b <-> b1 a < b1 b) -> (a < b <-> b1 a < b1 b)  | 
        
        
          | 4 | 
           | 
          ltsuc | 
          b0 a < b0 b <-> suc (b0 a) < suc (b0 b)  | 
        
        
          | 5 | 
          4 | 
          conv b1 | 
          b0 a < b0 b <-> b1 a < b1 b  | 
        
        
          | 6 | 
          3, 5 | 
          ax_mp | 
          a < b <-> b1 a < b1 b  | 
        
      
    
    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_peano
     (peano1,
      peano2,
      peano5,
      addeq,
      muleq,
      add0,
      addS,
      mul0,
      mulS)