Story, fairy tale, newspaper article, etc. A lot of small latin letters, and about 15% of another symbols. In fact it means that this text can be easily compressed by all the compression algorythms, i.g. Huffman, Shannon-Fano, Lempel-Ziv, etc.

In the prob statement, it's said that it can't contain digits. But a newspaper article usually does contain numbers. And, what punctuations can it have? Of course commas and periods are valid, but what about @, [], and ^? Are these possible?

Just use one of the algorithms mentioned above to compress a sequence of bytes. If your solution is bitshift-based (it is a kind of cheating), so you may assume the alphabet contains no more than 128 symbols.