No problem! We can import the same module twice but Angular does not like modules with circular references.
Stayed Informed - Angular 4 Docs
So do not let Module “X” import Module “Y” which already imports Module “X”.
When four modules all import Module “X”, Angular estimate Module “X” once, the first time face it and does not do again.
Actually, the modules help us to organize an application into associative blocks of functionality.
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