Question:
If a combat result is DH (assume the survivors can retreat to a hex not in an enemy ZOC), and the defending stack contains one or more zero strength units and/or position AA units, how does the DH result affect these zero-strength units?

Answer:
Since they have no strength to contribute to the defense, nor lose, they are not counted when considering strength point losses and therefore could not be taken as strength point losses. Zero strength point units are not affected by DH results, in so far as losses are considered; they must retreat, of course.

Followup Question:
Does the same principle hold for other combat results such as HX and AH?

Followup Answer:
Yes. Zero strength units contribute nothing to the numerical value of the units involved in the combat and half of nothing is still nothing.

Source:
TEM 76