Theorem msdcn

Description: The metric function of a metric space is always continuous in the topology generated by it. (Contributed by Mario Carneiro, 5-May-2014) (Revised by Mario Carneiro, 5-Oct-2015)

	Ref	Expression
Hypotheses	msdcn.x	|- X = ( Base ` M )
	msdcn.d	|- D = ( dist ` M )
	msdcn.j	|- J = ( TopOpen ` M )
	msdcn.2	|- K = ( topGen ` ran (,) )
Assertion	msdcn	|- ( M e. MetSp -> ( D |` ( X X. X ) ) e. ( ( J tX J ) Cn K ) )

Proof

Step	Hyp	Ref	Expression
1		msdcn.x	|- X = ( Base ` M )
2		msdcn.d	|- D = ( dist ` M )
3		msdcn.j	|- J = ( TopOpen ` M )
4		msdcn.2	|- K = ( topGen ` ran (,) )
5	1 2	msmet2	|- ( M e. MetSp -> ( D |` ( X X. X ) ) e. ( Met ` X ) )
6		eqid	|- ( MetOpen ` ( D |` ( X X. X ) ) ) = ( MetOpen ` ( D |` ( X X. X ) ) )
7	6 4	metdcn2	|- ( ( D |` ( X X. X ) ) e. ( Met ` X ) -> ( D |` ( X X. X ) ) e. ( ( ( MetOpen ` ( D |` ( X X. X ) ) ) tX ( MetOpen ` ( D |` ( X X. X ) ) ) ) Cn K ) )
8	5 7	syl	|- ( M e. MetSp -> ( D |` ( X X. X ) ) e. ( ( ( MetOpen ` ( D |` ( X X. X ) ) ) tX ( MetOpen ` ( D |` ( X X. X ) ) ) ) Cn K ) )
9	2	reseq1i	|- ( D |` ( X X. X ) ) = ( ( dist ` M ) |` ( X X. X ) )
10	3 1 9	mstopn	|- ( M e. MetSp -> J = ( MetOpen ` ( D |` ( X X. X ) ) ) )
11	10 10	oveq12d	|- ( M e. MetSp -> ( J tX J ) = ( ( MetOpen ` ( D |` ( X X. X ) ) ) tX ( MetOpen ` ( D |` ( X X. X ) ) ) ) )
12	11	oveq1d	|- ( M e. MetSp -> ( ( J tX J ) Cn K ) = ( ( ( MetOpen ` ( D |` ( X X. X ) ) ) tX ( MetOpen ` ( D |` ( X X. X ) ) ) ) Cn K ) )
13	8 12	eleqtrrd	|- ( M e. MetSp -> ( D |` ( X X. X ) ) e. ( ( J tX J ) Cn K ) )