Ruki sound law

The ruki sound law, also known as the ruki rule or iurk rule, refers to a historical sound change that took place in the satem branches of the Indo-European language family, namely in Balto-Slavic, Albanian, Armenian, 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, and the semi-vowels *w (*u̯) and *y (*i̯):

Specifically, the initial stage involves the retraction of the coronal sibilant *s after semi-vowels, *r, or a velar consonant *k or *g (developed from earlier *k, *g, *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 Indian 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.

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