You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: drop_nested_boxed_dyn.rs
    path of file: ./repos/kani/tests/kani/Drop
    
    the code of the file until where you have to start completion: // Copyright Kani Contributors
// SPDX-License-Identifier: Apache-2.0 OR MIT

// Check drop implementation for a nested boxed dynamic trait objects.
// There is an implicit self-recursive call to drop_in_place, so we
// need to set an unwind bound.

// cbmc-flags: --unwinding-assertions

static mut CELL: i32 = 0;

struct Concrete;

impl Drop for Concrete {
    fn drop(&
    
fn main() {
    // Check normal box
    {
        let _x: Box<dyn Send> = Box::new(Concrete {});
    }
    unsafe {
        assert!(CELL == 1);
    }

    // Reset global
    unsafe {
        CELL = 0;
    }

    // Check nested box, still only incremented once
    {
        let x: Box<dyn Send> = Box::new(Concrete {});
        let _nested: Box<dyn Send> = Box::new(x);
    }
    unsafe {
        assert!(CELL == 1);
    }
}