EIGRP Loop Prevention Logic

EIGRP Loop Prevention Logic:
Hamid sent me the following question:

I have already memorized (bad idea, BTW) that a loop can occur if FD < RD. Could you please tell me how a loop could occur assuming FD < RD and we ignore the feasibility condition.

I’ll use a simple three-router network (see the following diagram) to illustrate why EIGRP cannot figure out whether an alternate more expensive path could lead to a loop or not.
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