Any function for calculating inersect of intervals?

Hi,
wondering if exists any functions which aim to calculate intersect of two
intervals.
E.g. I have four dates (D1, D2, D3, D4) and I want to know if (D1,D2)
intersects (D3,D4) or not.

I konw that it can be done by comparing the dates (>=,<=), but I'm wonder if
I can do it simpler and shorter.

Thank you very much.

-- Csaba

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