theorem nffunc {x: nat} (F A B: set x):
  $ FS/ x F $ >
  $ FS/ x A $ >
  $ FS/ x B $ >
  $ F/ x func F A B $;
    
      
        | Step | Hyp | Ref | Expression | 
|---|
        
          | 1 |  | hyp hF | FS/ x F | 
        
          | 2 | 1 | nfisf | F/ x isfun F | 
        
          | 3 | 1 | nfdm | FS/ x Dom F | 
        
          | 4 |  | hyp hA | FS/ x A | 
        
          | 5 | 3, 4 | nfeqs | F/ x Dom F == A | 
        
          | 6 | 2, 5 | nfan | F/ x isfun F /\ Dom F == A | 
        
          | 7 | 1 | nfrn | FS/ x Ran F | 
        
          | 8 |  | hyp hB | FS/ x B | 
        
          | 9 | 7, 8 | nfss | F/ x Ran F C_ B | 
        
          | 10 | 6, 9 | nfan | F/ x isfun F /\ Dom F == A /\ Ran F C_ B | 
        
          | 11 | 10 | conv func | F/ x func F 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)