Fortunatov's law
Fortunatov's law is the observation, in the development of Indo-Aryan from Proto-Indo-European, that when *l is followed by a dental consonant, the dental becomes retroflex and the *l is deleted, eg. PIE *bʰelsos > Sanskrit bhā́ṣā, Lithuanian bal̃sas and PIE *poltos > Sanskrit paṭa, Greek péltē, Farsi parde. This law is not uniform.