The function f(x) takes an input word and applies a rule that results in a pair of words as the output. The rule seems to be a simple swapping of the input word with another word. Specifically, if the input word is "word1" and the output word is "word2", then the pair (word1, word2) is produced. Similarly, if the input word is "word2", then the pair (word2, word1) is produced.

