theorem sndleid (a: nat): $ snd a <= a $;
    
      
        | Step | Hyp | Ref | Expression | 
|---|
        
          | 1 |  | leeq2 | fst a, snd a = a -> (snd a <= fst a, snd a <-> snd a <= a) | 
        
          | 2 |  | fstsnd | fst a, snd a = a | 
        
          | 3 | 1, 2 | ax_mp | snd a <= fst a, snd a <-> snd a <= a | 
        
          | 4 |  | leprid2 | snd a <= fst a, snd a | 
        
          | 5 | 3, 4 | mpbi | snd a <= 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)