Recall can be computed with respect to unigram, bigram, trigram, or 4-gram matching. Each house begins with a hexagram made by doubling a trigram. The associated trigram of this "pumsae" is Yin. Symbolically, each form in the palgwae series corresponds to one trigram. Each trigram (gwae) corresponds to a natural element. IATA region codes trigram letters codes used to specify large territories, consisting of several countries. The trigram associated with this "pumsae" represents Wind. The trigram associated with this "pumsae" represents the Earth. The trigram associated with this "pumsae" represents a Mountain. The trigram associated with this "pumsae" represents Water. The associated trigram of this "pumsae" represents the Lake(joy, a calm sturdy spirit&colon;). First they selected a trigram from the K-Book, say YLA. It used a trigram index to speed queries. The eight process is repeated for the upper trigram. Using trigram statistics would further improve the chances of a correct guess.