x1 is the difficulty of Lojban word-making.
Cf. jbovlazbakemsedycro. Making words in Lojban is difficult in a variety of ways, depending on what type of word you're trying to make. Proper lujvo-making requires a good grasp of the semantics of the relevant gismu; and of tanru syntax, especially the scope of various grammatical constructs; knowledge of Lojban morphology and phonotactics to correctly insert y-hyphens where needed and avoid unparseable wordlike forms such as *tosmabru and *slinku'i (see valrtosmabru, valslinku'i); and finally, if you want to add your word to the dictionary, facility with the lujvo-scoring algorithm. Making Type 4 fu'ivla (or zi'evla), on the other hand, presents the challenge of knowing, out of hundreds of wordlike phonological patterns, which will parse as single-morpheme words and which will not. (For example, the nonce word kadvati will parse but *kazvati will not; fra'aso will but *fra'asoi will not; kadnazbakai will but kadnazbackai is a actually a lujvo.) Making Type 3 fu'ivla is comparatively easy, but still requires knowing how to use hyphen phonemes right and, of course, how to not violate phonotactical rules when lojbanizing foreign words. Luckily, the work of checking potential word forms can be mostly automated now, if you have access to sutysisku or jbovlaste.