Not genius. Experience. In the Bentley/Knuth/McIlroy paper I said, "[Old] Unix hands know instinctively how to solve this one in a jiffy." While that is certainly true, the script was informed by my having written "spell", which itself was an elaboration of a model pioneered by Steve Johnson. By 1986, when BKM was published, the lore was baked in: word-processing scripts in a similar vein were stock in trade. A very early exercise of this sort was Dennis Ritchie's enumeration of anagrams in the unabridged Merriam-Webster. Since the word list barely fit on the tiny disk of the time, the job entailed unimaginable marshalling of resources. I was mightily impressed then, and still am. Doug