Theorem basendx

Description: Index 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 Mario Carneiro, 2-Aug-2013)

	Ref	Expression
Assertion	basendx	|- ( Base ` ndx ) = 1

Proof

Step	Hyp	Ref	Expression
1		df-base	|- Base = Slot 1
2		1nn	|- 1 e. NN
3	1 2	ndxarg	|- ( Base ` ndx ) = 1