# If curve bn256/bls12 support the isomorphism from $G_2$ to $G_1$?

Is bn256 or bls12 a type-2 pairing-friendly curve?

As Dan Boneh said here

While in many pairing instantiations this ψ exists naturally, in some instantiations it does not.

However I can not find the isomorphism function in related library like bls12 and bn256.