Theorem s2len

Description: The length of a doubleton word. (Contributed by Stefan O'Rear, 23-Aug-2015) (Revised by Mario Carneiro, 26-Feb-2016)

	Ref	Expression
Assertion	s2len	$$⊢\left|⟨“AB”⟩\right|=2$$

Proof

Step	Hyp	Ref	Expression
1		df-s2	$$⊢⟨“AB”⟩=⟨“A”⟩\mathrm{++}⟨“B”⟩$$
2		s1cli	$$⊢⟨“A”⟩\in \mathrm{Word}\mathrm{V}$$
3		s1len	$$⊢\left|⟨“A”⟩\right|=1$$
4		1p1e2	$$⊢1+1=2$$
5	1 2 3 4	cats1len	$$⊢\left|⟨“AB”⟩\right|=2$$