Pinault's law

Pinault's law is a Proto-Indo-European phonological rule named after the French Indo-Europeanist Georges-Jean Pinault who discovered it.
According to this rule, PIE laryngeals disappear between an underlying non-syllabic consonant and *y. Examples can be seen in the formation of imperfective verbs by appending to the stem.
Compare:

PIE root 'to say' → imperfective 'to be saying'
PIE root 'to plow' → imperfective 'to be plowing'
PIE root 'to spin' → imperfective 'to be spinning'. Here the laryngeal /h₁/ is not deleted since it is preceded by a vowel.