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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