theorem zlt0sub (a b: nat): $ 0  b 
    
      
        | Step | Hyp | Ref | Expression | 
|---|
        
          | 1 |  | bitr3 | (0 +Z b <Z a <-> 0 <Z a -Z b) -> (0 +Z b <Z a <-> b <Z a) -> (0 <Z a -Z b <-> b <Z a) | 
        
          | 2 |  | zltaddsub | 0 +Z b <Z a <-> 0 <Z a -Z b | 
        
          | 3 | 1, 2 | ax_mp | (0 +Z b <Z a <-> b <Z a) -> (0 <Z a -Z b <-> b <Z a) | 
        
          | 4 |  | zlteq1 | 0 +Z b = b -> (0 +Z b <Z a <-> b <Z a) | 
        
          | 5 |  | zadd01 | 0 +Z b = b | 
        
          | 6 | 4, 5 | ax_mp | 0 +Z b <Z a <-> b <Z a | 
        
          | 7 | 3, 6 | ax_mp | 0 <Z a -Z b <-> b <Z 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)