Within the Indo-European language family, the Iranian branch stands closest to the Indo-Aryan branch (see dating in Blažek and Schwarz 2017: 236–237; Blažek and Hegedűs 2012), but with regard to sound change, it is closest to Slavic. Besides the merging of mediæ aspiratæ of the type d^h with mediæ of the type d into only d (also in Baltic, Celtic, and Albanian), it includes the RUKI rule (also in Indo-Aryan, partially…