Matasović, Ranko (2012). "A Grammatical Sketch of Albanian for students of Indo-European". Page 13:"It has been claimed that the difference between the three PIE series of gutturals is preserved in Albanian before front vowels. This thesis, sometimes referred to as Pedersen’s law, is often contested, but still supported by the majority of Albanologists (e. g. Hamp, Huld, and Ölberg). In examining this view, one should bear in mind that it seems certain that there were at least two palatalizations in Albanian: the first palatalization, whereby labiovelars were palatalized to s and z before front vowels and *y, and the second palatalization, whereby all the remaining velars (*k and *g) were palatalized to q and gj, in the same environment. PIE palatalized velars are affected by neither palatalization (they yield Alb. th, d, dh, cf. Alb. thom ‘I say’ < *k’ensmi, cf. OInd. śa m s- ‘praise’, L c e nse o ‘reckon’). It may be that th yielded f before a consonant, if Alb. ënfle ‘sleep’ is from *nthle < *n-k’loye- (cf. G klínō ‘recline’). "