theorem add11 (a: nat): $ 1 + a = suc a $;
    
      
        | Step | Hyp | Ref | Expression | 
        
          | 1 | 
           | 
          eqtr | 
          1 + a = suc (0 + a) -> suc (0 + a) = suc a -> 1 + a = suc a  | 
        
        
          | 2 | 
           | 
          addS1 | 
          suc 0 + a = suc (0 + a)  | 
        
        
          | 3 | 
          2 | 
          conv d1 | 
          1 + a = suc (0 + a)  | 
        
        
          | 4 | 
          1, 3 | 
          ax_mp | 
          suc (0 + a) = suc a -> 1 + a = suc a  | 
        
        
          | 5 | 
           | 
          suceq | 
          0 + a = a -> suc (0 + a) = suc a  | 
        
        
          | 6 | 
           | 
          add01 | 
          0 + a = a  | 
        
        
          | 7 | 
          5, 6 | 
          ax_mp | 
          suc (0 + a) = suc a  | 
        
        
          | 8 | 
          4, 7 | 
          ax_mp | 
          1 + a = 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)