How do I detect circular logic or recursion in a multi-levels references and dependencies

I have a graph of multi-level dependecies like this, and I need to detect any circular reference in this graph.

A = B

B = C

C = [D, B]

D = [C, A]

Somebody have a problem like this?

Any solution???

Thanks and sorry by english.

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I had another situation.

1

2 = 1

3 = 2

4 = [2, 3]

5 = 4

In this case, my recursive code iterate two times in "4" reference, but this references don't generate a infinite loop. My problem is to know when function iterate more than one time a reference and is not infinite loop and when is a infinite loop, to inform user.

1 = 4

2 = 1

3 = 2

4 = [2, 3]

5 = 4

This case is a bit diferent from 2th example. This generate a infinite loop. how can I know when cases generate a infinite loop or not?