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Metamath Proof Explorer

Theorem xmsge0

Description: The distance function in an extended metric space is nonnegative. (Contributed by Mario Carneiro, 4-Oct-2015)

Ref Expression
Hypotheses mscl.x 
|- X = ( Base ` M )
mscl.d 
|- D = ( dist ` M )
Assertion xmsge0 
|- ( ( M e. *MetSp /\ A e. X /\ B e. X ) -> 0 <_ ( A D B ) )

Proof

Step Hyp Ref Expression
1 mscl.x 
 |-  X = ( Base ` M )
2 mscl.d 
 |-  D = ( dist ` M )
3 1 2 xmsxmet2 
 |-  ( M e. *MetSp -> ( D |` ( X X. X ) ) e. ( *Met ` X ) )
4 xmetge0 
 |-  ( ( ( D |` ( X X. X ) ) e. ( *Met ` X ) /\ A e. X /\ B e. X ) -> 0 <_ ( A ( D |` ( X X. X ) ) B ) )
5 3 4 syl3an1 
 |-  ( ( M e. *MetSp /\ A e. X /\ B e. X ) -> 0 <_ ( A ( D |` ( X X. X ) ) B ) )
6 ovres 
 |-  ( ( A e. X /\ B e. X ) -> ( A ( D |` ( X X. X ) ) B ) = ( A D B ) )
7 6 3adant1 
 |-  ( ( M e. *MetSp /\ A e. X /\ B e. X ) -> ( A ( D |` ( X X. X ) ) B ) = ( A D B ) )
8 5 7 breqtrd 
 |-  ( ( M e. *MetSp /\ A e. X /\ B e. X ) -> 0 <_ ( A D B ) )