Howto detect that a Lua script is running on CORE?

Help
1

I would like to code

if (???) then
-- Code which is intended to run specially on CORE ( e.g. special references to CORE objects )
else
-- Code which is not intended to run on CORE ( e.g. the standard "require()",..)
end

How to do this?

I guessed that I might do it with "os" library functions, but I did not get a clue.

Sincerely
Rolf