With monoalphabetic substitutions, you can run the plaintext through as many encryptions as you want but the finished product will be as weak as if you’d done it once.

Similarly, transposition or double transposition cannot change the letter frequencies of a piece of ciphertext. 

Double Transposition

 Maybe K4 has some transposition element(s) in it but these have been used in conjunction with another method that has changed the identity of the plaintext letters.

Kryptosfan

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