I'm writing a thesis focused on Maurer's provably-secure stream cipher. Long story short, this cipher works by expanding a short key into a long keystream and then XORring this keystream with the plaintext in order to obtain the ciphertext (and vicecersa).
Take this definition of a binary-additive stream cipher: a cipher where the plaintext, ciphertext and keystream are binary strings and where the ciphertext is produced as a XOR addition of the plaintext and the keystream.
Also, take this definition of a reciprocal cipher: a cipher in which the encryption and decryption algorithms are identical (they're the same involution).
With these two definitions, can I state that binary-additive stream ciphers are all reciprocal ciphers? I think so, since if the ciphertext is the XOR of plaintext and keystream, than the plaintext must be the XOR of the keystream and the ciphertext.