Is there a law that prohibits PIE stems starting with what traditionally reconstructed as non-palatal /g/?
So far I encountered with only one stem that the sources consistently reconstruct with this phoneme: ġloiu̯os "clay" (here ġ denotes non-palatal, possibly uvular g). Is this stem reconstructed reliably? Cannot it be a borrowing?
Note that I know about a prohibition on stems starting with "r-".