theorem mulrass (a b c: nat): $ a * b * c = a * c * b $;
    
      
        | Step | Hyp | Ref | Expression | 
|---|
        
          | 1 |  | eqtr | a * b * c = a * (b * c) -> a * (b * c) = a * c * b -> a * b * c = a * c * b | 
        
          | 2 |  | mulass | a * b * c = a * (b * c) | 
        
          | 3 | 1, 2 | ax_mp | a * (b * c) = a * c * b -> a * b * c = a * c * b | 
        
          | 4 |  | eqtr4 | a * (b * c) = a * (c * b) -> a * c * b = a * (c * b) -> a * (b * c) = a * c * b | 
        
          | 5 |  | muleq2 | b * c = c * b -> a * (b * c) = a * (c * b) | 
        
          | 6 |  | mulcom | b * c = c * b | 
        
          | 7 | 5, 6 | ax_mp | a * (b * c) = a * (c * b) | 
        
          | 8 | 4, 7 | ax_mp | a * c * b = a * (c * b) -> a * (b * c) = a * c * b | 
        
          | 9 |  | mulass | a * c * b = a * (c * b) | 
        
          | 10 | 8, 9 | ax_mp | a * (b * c) = a * c * b | 
        
          | 11 | 3, 10 | ax_mp | a * b * c = a * c * 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_peano
     (peano2,
      peano5,
      addeq,
      muleq,
      add0,
      addS,
      mul0,
      mulS)