void main ( ) {
    int y=1;
    void C( ) {
        void D( ) {
            int y=4;      // stop here
        }
        D( );
    }
    void A(int f) {
        int z=2;
        void B( ) {
            int x=3;
            A(x-y-z);
        }
        if (f) {
            B( );
        } else {
            C( );
        }
    }
    A(y);
}

Things to show:
- activation stack at 'stop here'
- scope of global y using static scoping rules
- referencing environment at 'stop here'
   - using static scoping rules
   - using dynamic scoping rules