Why I cannot purge mono-devel on Ubuntu Linux 16.04?

[Frank Chang]

    After sudo apt-get install mono-devel , when I try to purge mono-devel
on Ubuntu Linux 16.04, I get the following error message

Reading package lists... Done
Building dependency tree
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
mono-devel : Depends: mono-runtime (>= 2.10.1) but it is not installable
              Depends: libmono-cecil-private-cil (>= 2.6.3) but it is not
going to be installed
              Depends: libmono-codecontracts4.0-cil (>= 1.0) but it is not
going to be installed
              Depends: libmono-compilerservices-symbolwriter4.0-cil (>=
1.0) but it is not going to be installed
              Depends: libmono-corlib2.0-cil (>= 2.6.3) but it is not going
to be installed
              Depends: libmono-corlib4.0-cil (>= 2.10.1) but it is not
going to be installed
              Depends: libmono-peapi2.0-cil (>= 2.4.2) but it is not going
to be installed

etc...
    Why does this error occur and how can I fix it?


    Also, is it necessary to install mono-devel for a production system? I
understand that mono-devel
 contains various development tools and pulls in the default development
stack for Mono .

    We may be using mono-devel for C#/ASP.NET webforms compilation and
development.

   Any help is greatly appreciated.

   Thank you.
       Frank
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