Whether to include the definite article when we talk about all of the instances of some set

Question

a. k. a., i. e., e. g. — Notice that the intermediate periods in the abbreviations are followed by hair spaces.

The sentence after the abbreviations themselves is not a description of a rule how abbreviations should be typed. It is description about how these three particular examples are typed.

Is it correct in such a case to follow "that" with "the" or the article should be omitted?

Notice that intermediate periods in the abbreviations are followed by hair spaces.

My understanding of grammar rules tells me to include the article, but for some reason it sounds odd.

Answer 1

These are periods well-defined by this context, so the definite article should be used. To further emphasise this point, you might wanna use THESE abbreviations instead of THE abbreviations... if this matches your idea.

a. k. a., i. e., e. g. — Notice that the intermediate periods in the/these abbreviations are followed by hair spaces.