Let us start with computer code. We take computer code as a well-formed3 se- quence of instructions in a Turing-complete language. Since such instructions are mere sequences of symbols, the identity of code is defined accordingly: two codes are identi- cal if and only if they have exactly the same syntactic structure. So, any syntactic change in a code c1 results in a different code c2. These changes may include variable renaming, order changes in declarative definitions, inclusion and deletion of comments, etc.