Ad. voiceless stops became spirants before homorganic spirants; [pf|tθ|kx] > [ff|θθ|xx]

Ad. voiceless stops became spirants before homorganic spirants; [pf|tθ|kx] > [ff|θθ|xx]
At the same time as aspirates became voiceless spirants, voiceless stops appearing before aspirates of the same series became first affricates and then double spirants (SD/419). The primitive combinations influenced in this way were ✶[ppʰ], ✶[ttʰ] and ✶[kkʰ], which became [ff], [θθ] and [xx], respectively.

Reference ✧ SD/419 ✧ for example: FF < PF < ✶Ad. PPh, ÞÞ < < ✶Ad. TTh, XX < KX < ✶Ad. KKh

Related

Phonetic Rule Elements

[pf] > [ff] ✧ SD/419 (PPh > PF > FF)
[tθ] > [θθ] ✧ SD/419 (TTh > > ÞÞ)
[kx] > [xx] ✧ SD/419 (KKh > KX > XX)