Which of these statements are true regarding shift cipher?

Multiple select question.

For the shift cipher f$($p$)=$ p $+13$ mod $26,$ the encryption function is the same as the decryption function.

There are $26$ different shift ciphers counting the one that leaves messages unchanged.

For the shift cipher f$($p$)=$ p $+25$ mod $26,$ the encryption function is the same as the decryption function.

Decryption of ciphertext produced by the shift cipher

f$($p$)=$ p $+$ k mod $26$ can be decrypted using the function d$($p$)=$ p $+(26$ k$)$ mod $26.$

The encryption function f$($p$)=-$p $+13$ mod $26$ is a shift cipher.