Theorem cshw1repsw

Description: If cyclically shifting a word by 1 position results in the word itself, the word is a "repeated symbol word". Remark: also "valid" for an empty word! (Contributed by AV, 8-Nov-2018) (Proof shortened by AV, 10-Nov-2018)

	Ref	Expression
Assertion	cshw1repsw	|- ( ( W e. Word V /\ ( W cyclShift 1 ) = W ) -> W = ( ( W ` 0 ) repeatS ( # ` W ) ) )

Proof

Step	Hyp	Ref	Expression
1		cshw1	|- ( ( W e. Word V /\ ( W cyclShift 1 ) = W ) -> A. i e. ( 0 ..^ ( # ` W ) ) ( W ` i ) = ( W ` 0 ) )
2		repswsymballbi	|- ( W e. Word V -> ( W = ( ( W ` 0 ) repeatS ( # ` W ) ) <-> A. i e. ( 0 ..^ ( # ` W ) ) ( W ` i ) = ( W ` 0 ) ) )
3	2	bicomd	|- ( W e. Word V -> ( A. i e. ( 0 ..^ ( # ` W ) ) ( W ` i ) = ( W ` 0 ) <-> W = ( ( W ` 0 ) repeatS ( # ` W ) ) ) )
4	3	adantr	|- ( ( W e. Word V /\ ( W cyclShift 1 ) = W ) -> ( A. i e. ( 0 ..^ ( # ` W ) ) ( W ` i ) = ( W ` 0 ) <-> W = ( ( W ` 0 ) repeatS ( # ` W ) ) ) )
5	1 4	mpbid	|- ( ( W e. Word V /\ ( W cyclShift 1 ) = W ) -> W = ( ( W ` 0 ) repeatS ( # ` W ) ) )