PIE word formation

I would like to open a thread in which to fix 'more exactly' the PIE
word formation rules

I will start proposing a very general rool , in order to can refine it
next (I'm still not sure that is the correct one)

pie_word -> pie_root
( thematic_vowel
pie_sufix
)*
pie_ending?


where -> - means 'is defined as'
(x)* - x can appear zero-times till n-times
(x)+ - x can appear one-time till n-times
(x)? - x can appear one time or not at all
a b - means 'a and b'
a | b - means 'a or b'
the notation is that what of language grammars
I will add later grammar attributes notations too, if the topic will
survive

Thanks in advance for joining this topic.

Marius