theorem ljoineq (_L1 _L2: nat): $ _L1 = _L2 -> ljoin _L1 = ljoin _L2 $;
    
      
        | Step | Hyp | Ref | Expression | 
        
          | 1 | 
           | 
          id | 
          _L1 = _L2 -> _L1 = _L2  | 
        
        
          | 2 | 
          1 | 
          ljoineqd | 
          _L1 = _L2 -> ljoin _L1 = ljoin _L2  | 
        
      
    
    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
     (peano2,
      addeq,
      muleq)