theorem sucb1 (a: nat): $ suc (b1 a) = b0 (suc a) $;
    
      
        | Step | Hyp | Ref | Expression | 
|---|
        
          | 1 |  | eqtr2 | b0 (suc a) = suc (a + suc a) -> suc (a + suc a) = suc (b1 a) -> suc (b1 a) = b0 (suc a) | 
        
          | 2 |  | addS1 | suc a + suc a = suc (a + suc a) | 
        
          | 3 | 2 | conv b0 | b0 (suc a) = suc (a + suc a) | 
        
          | 4 | 1, 3 | ax_mp | suc (a + suc a) = suc (b1 a) -> suc (b1 a) = b0 (suc a) | 
        
          | 5 |  | suceq | a + suc a = b1 a -> suc (a + suc a) = suc (b1 a) | 
        
          | 6 |  | addS | a + suc a = suc (a + a) | 
        
          | 7 | 6 | conv b0, b1 | a + suc a = b1 a | 
        
          | 8 | 5, 7 | ax_mp | suc (a + suc a) = suc (b1 a) | 
        
          | 9 | 4, 8 | ax_mp | suc (b1 a) = b0 (suc 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_peano
     (peano2,
      peano5,
      addeq,
      add0,
      addS)