Greeklish may be orthographic or phonetic. In orthographic use, the intent is to reproduce Greek orthography closely: there is a one-to-one mapping between Greek and Latin letters, and digraphs are avoided, with occasional use of punctuation or numerals resembling Greek letters rather than Latin digraphs. While letters are in the first instance chosen for phonetic similarity, visual equivalence, and corresponding keyboard keys, are used when phonetically similar letters are exhausted. Thus, psi (ψ) may be written as ps, 4 or y; xi (ξ) as ks, x or 3; and theta (θ) as th or 8.