Mimic function

A mimic function changes a file formula_1 so it assumes the statistical properties of another file formula_2. That is, if formula_3 is the probability of some substring formula_4 occurring in formula_1, then a mimic function formula_6, recodes formula_1 so that formula_8 approximates formula_9 for all strings formula_4 of length less than some formula_11. It is commonly considered to be one of the basic techniques for hiding information, often called steganography. 
The simplest mimic functions use simple statistical models to pick the symbols in the output. If the statistical model says that item formula_12 occurs with probability formula_13 and item formula_14 occurs with probability formula_15, then a random number is used to choose between outputting formula_12 or formula_14 with probability formula_13 or formula_15 respectively.
Even more sophisticated models use reversible Turing machines.