A significant part of “concise syntax” of kotlin is moved from the language itself to the standard library, so it is mostly unusable without it. You can call java types directly like java.util.Map, but still you will miss most of the things that make kotlin kotlin. I am not sure, why do you need to remove kotlin stdlib, If you want to s limit the size of the package, then standard tools like proguard or R8 will reduce the overhead of compiled code size almost to zero.
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