Many thanks, Leopold! 
It seems to me it succeeds now.
I will show the result after some time.
Hello.
I created definition with sorting on the shortest line and experimented with yours.
But as the practice showed, the triangle is often formed, but not always.
After observing the corners of the opposite lines, I found the pattern that the triangle is always formed from the side of the smallest corner.
I began to write a new definition. I sorted, combined the opposite lines into groups and calculated their corners. But nothing comes to mind how to sort these two groups on the smallest corner to continue working.
Can you help to sort if you know how?
Sort by angle.gh (24.3 KB)
The triangle is there but you can’t see it.
I believe that the only solution is to evaluate the four possibilities and choose the best one.
Offset with a factor f.gh (15.7 KB)
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Leopold, I’m deeply grateful for your support.
It’s all done.
Offset_4 point.gh (12.7 KB)