Theorem s8len

Description: The length of a length 8 string. (Contributed by Mario Carneiro, 26-Feb-2016)

	Ref	Expression
Assertion	s8len	|- ( # ` <" A B C D E F G H "> ) = 8

Proof

Step	Hyp	Ref	Expression
1		df-s8	|- <" A B C D E F G H "> = ( <" A B C D E F G "> ++ <" H "> )
2		s7cli	|- <" A B C D E F G "> e. Word _V
3		s7len	|- ( # ` <" A B C D E F G "> ) = 7
4		7p1e8	|- ( 7 + 1 ) = 8
5	1 2 3 4	cats1len	|- ( # ` <" A B C D E F G H "> ) = 8