Remove PublicKeyPair struct and refer to R and R_prime directly
Notes
While PublicKeyPair has nothing to do in the DoubleSignature: R and R' are not a PublicKeyPair they are two nonce points.
Where it actually makes sense is in the public keys in order to verify a DoubleSignature (just like a PublicKey verifies a Signature a PublicKeyPair would verify a DoubleSignature).
Summary
Remove
PublicKeyPairstruct and refer toRandR_primedirectlyNotes
While
PublicKeyPairhas nothing to do in theDoubleSignature:RandR'are not aPublicKeyPairthey are twononcepoints. Where it actually makes sense is in the public keys in order to verify aDoubleSignature(just like aPublicKeyverifies aSignatureaPublicKeyPairwould verify aDoubleSignature).Relevant Context
see #81