the alveolars t and n, which, in turn, have also partially merged with velars c and ng in the Central and the Southern varieties. In addition to the regional variation described above, there is a merger of l and n in certain rural varieties in the North: Variation between l and n can be found even in mainstream Vietnamese in certain words. For example, the numeral "five" appears as năm by itself and in compound numerals like năm mươi "fifty," but it appears as in "fifteen" (see Vietnamese grammar#Cardinal). In some northern varieties, the numeral appears with an initial nh instead of l: "twenty-five", instead of the mainstream . There is also a merger of r and g in certain rural varieties in the South: The consonant clusters that were originally present in Middle Vietnamese (in the 17th century) have been lost in almost all modern Vietnamese varieties although they have been retained in other closely-related Vietic languages. However, some speech communities have preserved some of these archaic clusters: "sky" is with a cluster in Hảo Nho (Yên Mô, Ninh Bình Province) but trời in Southern Vietnamese and in Hanoi Vietnamese (initial single consonants , respectively). Tones Although there are six tones in Vietnamese, some tones may slightly merge but are still highly distinguishable from the context of the speech. The hỏi and ngã tones are distinct in North and some North-Central varieties (although often with different pitch contours) but have somewhat merged in the Central, Southern, and some North-Central varieties (also with different pitch contours). Some North-Central varieties (such as Vietnamese) have a slight merger of the ngã and nặng tones but keep the hỏi tone distinct. Still, other North-Central varieties have a three-way merger of hỏi, ngã, and nặng and so have a four-tone system. In addition, there are several phonetic differences (mostly in pitch contour and phonation type) in the tones among the dialects. The table above shows the pitch contour of each tone using Chao tone number notation in which 1 represents the lowest pitch, and 5 the highest; glottalization (creaky, stiff, harsh) is indicated with the symbol; murmured voice with ; glottal stop with ; sub-dialectal variants are separated with commas. (See also the tone section below.) Word play A basic form of word play in Vietnamese involves disyllabic words in which the last syllable forms the first syllable of the next word in the