Theorem baseval

Description: Value of the base set extractor. (Normally it is preferred to work with ( Basendx ) rather than the hard-coded 1 in order to make structure theorems portable. This is an example of how to obtain it when needed.) (New usage is discouraged.) (Contributed by NM, 4-Sep-2011)

	Ref	Expression
Hypothesis	baseval.k	$$⊢K\in \mathrm{V}$$
Assertion	baseval	$$⊢{\mathrm{Base}}_K=K\left(1\right)$$

Proof

Step	Hyp	Ref	Expression
1		baseval.k	$$⊢K\in \mathrm{V}$$
2		df-base	$$⊢\mathrm{Base}=\mathrm{Slot}1$$
3	1 2	strfvn	$$⊢{\mathrm{Base}}_K=K\left(1\right)$$