Theorem bj-pr1eq

Description: Substitution property for pr1 . (Contributed by BJ, 6-Apr-2019)

	Ref	Expression
Assertion	bj-pr1eq	|- ( A = B -> pr1 A = pr1 B )

Proof

Step	Hyp	Ref	Expression
1		bj-projeq2	|- ( A = B -> ( (/) Proj A ) = ( (/) Proj B ) )
2		df-bj-pr1	|- pr1 A = ( (/) Proj A )
3		df-bj-pr1	|- pr1 B = ( (/) Proj B )
4	1 2 3	3eqtr4g	|- ( A = B -> pr1 A = pr1 B )