Multiple copies (or an array or list) of the service in NgModule.
On StackOverflow, Gunter’s many, many comments are all correct.
A reason to follow his suggestions is that to build your desired pairing, it’ll be very difficult for others to read the code. After all, your S/O project isn’t laying out the M-D design pattern. It’s laying out M-D-M-D-M-D… and that’s messy. …Or are you going for TableOfContents-Master-Detail? It’s ambiguous.