Q. They didnt use to allow such goings-on here.
A. didnt use used not√. Inelegant form of verb used, though the expression (didnt use) is frequently used by inelegant speakers.

Inelegant speakers must make up over 90% of the population, then. used not sounds odd these days to most people.
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I havent understood what has been mentioned in the above text thus far because I am not familiar with the word "
inelegant" although I have checked the dictionary. As a result, according to the above explanation, what is the difference between the following pairs, please?

I didnt use to smoke.

I used not to smoke.