| Mathbox for Mykola Mostovenko | 
      
      
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| Description: Heyting's formal system Axiom #1 from [Heyting] p. 127. (Contributed by MM, 11-Aug-2018.) | 
| Ref | Expression | 
|---|---|
| ax1hfs | 
 | 
| Step | Hyp | Ref | Expression | 
|---|---|---|---|
| 1 | ax-ia3 108 | 
. 2
 | |
| 2 | 1 | pm2.43i 49 | 
1
 | 
| Colors of variables: wff set class | 
| Syntax hints:     | 
| This theorem was proved from axioms: ax-mp 5 ax-1 6 ax-2 7 ax-ia3 108 | 
| This theorem is referenced by: (None) | 
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