In a Math.SE question, I used the sentence:
“some two of these propositions are true and the third one is false”, or in other words, “exactly 2 of 3 propositions are true”
Here I used “or in other words” to rephrase a statement for better comprehension, but I didn’t use a comma after “or”. On the Net, I see people both using and omitting the comma in that phrase. What is the correct punctuation in the phrase “or in other words” and why?