 An example is the digits of the mathematical constant "pi", which appear random but can be generated by a very small program.However, even though it cannot be determined whether a particular file is incompressible, a simple theorem about incompressible strings shows that over 99% of files of any given length cannot be compressed by more than one byte (including the size of the decompressor).Abstractly, a compression algorithm can be viewed as a function on sequences (normally of octets).