Ruki sound law

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The ruki sound law, also known as the ruki rule or iurk rule, is a historical sound change that took place in the satem branches of the Indo-European language family, namely in Balto-Slavic, Armenian,^[1] and Indo-Iranian. According to this sound law, an original *s changed to *š (a sound similar to English ⟨sh⟩) after the consonants *r, *k, *g, *gʰ and the semi-vowels *w (*u̯) and *y (*i̯), as well as the syllabic allophones *r̥, *i, and *u:

*s > *š / {*r, *w, *K, *y} _

Specifically, the initial stage involves the retraction of the coronal sibilant *s after semi-vowels, *r, or a velar consonant *k, *g or *gʰ. In the second stage, leveling of the sibilant system resulted in retroflexion (cf. Sanskrit ष [ʂ] and Proto-Slavic), and later retraction to velar *x in Slavic and some Middle Indic languages. This rule was first formulated by Holger Pedersen, and it is sometimes known as Pedersen's law, although this term is also applied to another sound law concerning stress in the Balto-Slavic languages.

The name "ruki" comes from the sounds (r, u, K, i) which triggered the sound change. The law is stated as a mnemonic rule because the word руки means 'hands, arms' in Russian, or is the genitive singular form ('of the hand') of рука (compare rule of thumb).