Thorn clusters presented a problem in the reconstruction of some cognate sets in which Indo-Iranian sibilants in clusters with dorsals exceptionally correspond to coronal stops in certain other branches (particularly the Hellenic languages). 'Bear' and 'decaying' above are examples; another is Sanskrit "tákṣan" 'artisan' vs. Greek "téktōn" 'carpenter'. As was the case with the laryngeal theory, these cognate sets were first noted prior to the connection of Anatolian and Tocharian to PIE, and early reconstructions posited a new series of consonants to explain these correspondences. Brugmann 1897's systematic explanation augmented the PIE consonant system with a series of interdentals (nowhere directly attested) appearing only in clusters with dorsals, *kþ *kʰþʰ *gð *gʰðʰ. The use of the letter thorn led to the name "thorn cluster" for these groups.