theorem appendcan2 (a b c: nat): $ a ++ c = b ++ c <-> a = b $;
    
      
        | Step | Hyp | Ref | Expression | 
        
          | 1 | 
           | 
          bitr3 | 
          (rev (a ++ c) = rev (b ++ c) <-> a ++ c = b ++ c) -> (rev (a ++ c) = rev (b ++ c) <-> a = b) -> (a ++ c = b ++ c <-> a = b)  | 
        
        
          | 2 | 
           | 
          revinj | 
          rev (a ++ c) = rev (b ++ c) <-> a ++ c = b ++ c  | 
        
        
          | 3 | 
          1, 2 | 
          ax_mp | 
          (rev (a ++ c) = rev (b ++ c) <-> a = b) -> (a ++ c = b ++ c <-> a = b)  | 
        
        
          | 4 | 
           | 
          bitr | 
          (rev (a ++ c) = rev (b ++ c) <-> rev c ++ rev a = rev c ++ rev b) -> (rev c ++ rev a = rev c ++ rev b <-> a = b) -> (rev (a ++ c) = rev (b ++ c) <-> a = b)  | 
        
        
          | 5 | 
           | 
          eqeq | 
          rev (a ++ c) = rev c ++ rev a -> rev (b ++ c) = rev c ++ rev b -> (rev (a ++ c) = rev (b ++ c) <-> rev c ++ rev a = rev c ++ rev b)  | 
        
        
          | 6 | 
           | 
          revappend | 
          rev (a ++ c) = rev c ++ rev a  | 
        
        
          | 7 | 
          5, 6 | 
          ax_mp | 
          rev (b ++ c) = rev c ++ rev b -> (rev (a ++ c) = rev (b ++ c) <-> rev c ++ rev a = rev c ++ rev b)  | 
        
        
          | 8 | 
           | 
          revappend | 
          rev (b ++ c) = rev c ++ rev b  | 
        
        
          | 9 | 
          7, 8 | 
          ax_mp | 
          rev (a ++ c) = rev (b ++ c) <-> rev c ++ rev a = rev c ++ rev b  | 
        
        
          | 10 | 
          4, 9 | 
          ax_mp | 
          (rev c ++ rev a = rev c ++ rev b <-> a = b) -> (rev (a ++ c) = rev (b ++ c) <-> a = b)  | 
        
        
          | 11 | 
           | 
          bitr | 
          (rev c ++ rev a = rev c ++ rev b <-> rev a = rev b) -> (rev a = rev b <-> a = b) -> (rev c ++ rev a = rev c ++ rev b <-> a = b)  | 
        
        
          | 12 | 
           | 
          appendcan1 | 
          rev c ++ rev a = rev c ++ rev b <-> rev a = rev b  | 
        
        
          | 13 | 
          11, 12 | 
          ax_mp | 
          (rev a = rev b <-> a = b) -> (rev c ++ rev a = rev c ++ rev b <-> a = b)  | 
        
        
          | 14 | 
           | 
          revinj | 
          rev a = rev b <-> a = b  | 
        
        
          | 15 | 
          13, 14 | 
          ax_mp | 
          rev c ++ rev a = rev c ++ rev b <-> a = b  | 
        
        
          | 16 | 
          10, 15 | 
          ax_mp | 
          rev (a ++ c) = rev (b ++ c) <-> a = b  | 
        
        
          | 17 | 
          3, 16 | 
          ax_mp | 
          a ++ c = b ++ c <-> a = 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_set
     (elab,
      ax_8),
    
axs_the
     (theid,
      the0),
    
axs_peano
     (peano1,
      peano2,
      peano5,
      addeq,
      muleq,
      add0,
      addS,
      mul0,
      mulS)