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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def sign_with_privkey( digest: bytes, privkey: Ed25519PrivateKey, global_pubkey: Ed25519PublicPoint, nonce: int, global_commit: Ed25519PublicPoint, ) -> Ed25519Signature: """Create a CoSi signature of `digest` with the supplied private key. This function needs to know the global public key and global commitment. """

    h = _ed25519.H(privkey)
    a = _ed25519.decodecoord(h)

    S = (nonce + _ed25519.Hint(global_commit + global_pubkey + digest) * a) % _ed25519.l
    return Ed25519Signature(_ed25519.encodeint(S))