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I know the difference in the meaning between "regret + gerund" and "regret + infinitive"

(A) regret + doing: feel sorry about what I did in the past.
(B) regret + to do: feel sorry about what I will do now.

However, I don't exactly understand what difference exists in the below two sentences.
Could you please explain it to me?

(A) I regret not working harder.
(B) I regret not having worked harder.
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myidHowever, I don't exactly understand what difference exists in the below two sentences below.
Could you please explain it to me?

(A) I regret not working harder.
(B) I regret not having worked harder.
In actual usage there's no real difference. Theoretically, the present gerund (working) could refer to the present time and the future as well, but one can hardly regret anything that one hasn't yet done or is doing at this very moment.

CB
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It's very commendable to know gerunds, infinitives (split or otherwise) pronouns etc., etc., and all the correct grammatical terms and usages, but I sometimes think intelligent people, such as yourself, should ease up on the academic pursuit of grammatical terminology and just step back for a moment and, as Obi-Wan Kenobi might say to Luke Skywalker, 'feel the force' by just 'feeling' the sentences.

(A) Is present tense,'working' is the clue; it's not be too late to put the matter right.

- I regret not working harder, because I might have finished digging this hole today, instead I now find I will have to return tomorrow to finish it off.

(B) Is past tense, 'worked' is the clue; it's too late to put the matter right.

- I regret not having worked harder, because the exam is due in one hour and I haven't studied all the textbooks I was supposed to.

But as has been mentioned, both sentences are used willy-nilly, without thought.
(A) ; it's not be too late to put the matter right.

Sorry, typo - My error. Should have read: (A) ; it's not too late to put the matter right.