Appendix:Proto-Indo-European/ātr-
As mentioned by Benjamin W. Fortson the cover symbol H is used for a laryngeal that cannot or need not be specified, so we can surely use *HeHt(e)r- or *HeHt- for the entry. However, we've 2 other options which can work:
- *h₂eh₁ter- ("fireplace") - (https://www.academia.edu/16690811/2000_PIE_roots_summary_The_Source_Code_2.4_-_Excel)
- *hₓehₓtr- ("fire", in *hₓehₓt- at least one laryngeal was h₂ (> *h₂ehₓtr-), perhaps both - p.202) - (https://books.google.com/books?id=tzU3RIV2BWIC) | Michael A. Cahill also lists *hₓehₓtr-.
However Schrijver argues that:
- "Since it is unlikely that all these forms contain an unmotivated lengthened grade root *h₂et-, a reconstruction *HeHt- is attractive." - (https://books.google.com/books?id=0lNfAAAAMAAJ&focus=searchwithinvolume&q=*HeHt%28e%29r-)
- ătrōx, āter, and ātarš contain the zero grade of the root *HeHt-. - (http://institucional.us.es/revistas/habis/38/10%20zavaroni.pdf)
The specific origins of Etr. *atr-, Lat. āter/ātro-/ătrōx, Alb. votrë/votër, OIr. áith, Slav. vatra, and Av. ātarš can be then mentioned in the Etymology section. It looks like that even Baltic forms exist. According to this paper, *H3 is the standard symbol for *Hʷ. What does this mean acutally for *Hʷet-, *Hʷet˖r-?
We use lower-case h when we know which laryngeal it is, and upper-case H when we don't (h₁, h₂ and h₃, vs. H). It's inconsistent to mix an upper-case form like Hʷ with lower-case forms like hₓ: the paper you linked to seems to consistently use upper case for everything, so case doesn't mean anything in that context, and doesn't have to be followed. As for the *Hʷ notation itself, the problem is that it makes it look like it could be any laryngeal, but with rounding added, rather than a specific unknown sound that has the property of sometimes causing adjacent vowels to become rounded. I would convert your to notation to ours like this:
- hₓ = H
- Hʷ = h₃
Thus, *Hʷet- would be our h₃et-
Thank you for this introduction. So which reconstruction would you most prefer then? *h₂eh₁ter-, *h₂eh₂ter-, *h₂eHtr-, *HeHtr-, *HeHt(e)r-, *Hḕt-, *h₃et˖r- or *h₃et-?
I'm more familiar with the conventions used by our PIE entries than I am with the intricacies of laryngeal theory itself. I'll let CodeCat answer that