Theorem iccen

Description: Any nontrivial closed interval is equinumerous to the unit interval. (Contributed by Mario Carneiro, 26-Jul-2014) (Revised by Mario Carneiro, 8-Sep-2015)

	Ref	Expression
Assertion	iccen	|- ( ( A e. RR /\ B e. RR /\ A < B ) -> ( 0 [,] 1 ) ~~ ( A [,] B ) )

Proof

Step	Hyp	Ref	Expression
1		ovex	|- ( 0 [,] 1 ) e. _V
2		ovex	|- ( A [,] B ) e. _V
3		eqid	|- ( x e. ( 0 [,] 1 ) |-> ( ( x x. B ) + ( ( 1 - x ) x. A ) ) ) = ( x e. ( 0 [,] 1 ) |-> ( ( x x. B ) + ( ( 1 - x ) x. A ) ) )
4	3	iccf1o	|- ( ( A e. RR /\ B e. RR /\ A < B ) -> ( ( x e. ( 0 [,] 1 ) |-> ( ( x x. B ) + ( ( 1 - x ) x. A ) ) ) : ( 0 [,] 1 ) -1-1-onto-> ( A [,] B ) /\ `' ( x e. ( 0 [,] 1 ) |-> ( ( x x. B ) + ( ( 1 - x ) x. A ) ) ) = ( y e. ( A [,] B ) |-> ( ( y - A ) / ( B - A ) ) ) ) )
5	4	simpld	|- ( ( A e. RR /\ B e. RR /\ A < B ) -> ( x e. ( 0 [,] 1 ) |-> ( ( x x. B ) + ( ( 1 - x ) x. A ) ) ) : ( 0 [,] 1 ) -1-1-onto-> ( A [,] B ) )
6		f1oen2g	|- ( ( ( 0 [,] 1 ) e. _V /\ ( A [,] B ) e. _V /\ ( x e. ( 0 [,] 1 ) |-> ( ( x x. B ) + ( ( 1 - x ) x. A ) ) ) : ( 0 [,] 1 ) -1-1-onto-> ( A [,] B ) ) -> ( 0 [,] 1 ) ~~ ( A [,] B ) )
7	1 2 5 6	mp3an12i	|- ( ( A e. RR /\ B e. RR /\ A < B ) -> ( 0 [,] 1 ) ~~ ( A [,] B ) )