As the title says, code can't be a prefix-code and can't be a suffix-code, but it must be uniquely decodable. One possible code is this: {1, 101, 1001, ... }. Number of zeroes corresponds to the index of the letter in a given alphabet (starting from 0). Clearly it's not p-code and not a s-code and it's uniquely decodable. But I need to find another example of such code. And no, I wont accept {0, 010, 0110, ...}. By the way, code words must consist of 0 and 1, i.e. be binary.
An example of a code that is neither p-code or s-code but is uniquely decodable?
information theory