// visible inside the defining assembly only
internal class Foo;

// visible outside the defining assembly
public class Bar
{
    // visible outside the defining assembly
    // but foo is only available internally
    // so error
    public Foo GetFoo()
    {
        return new Foo();
    }

    // visible internally only
    // so no error
    internal Foo GetFoo()
    {
        return new Foo();
    }
}

// visible inside the defining assembly only
internal class Foo;

// visible outside the defining assembly
public class Bar
{
    // visible outside the defining assembly
    // but foo is only available internally
    // so error
    public Foo GetFoo()
    {
        return new Foo();
    }

    // visible internally only
    // so no error
    internal Foo GetFoo()
    {
        return new Foo();
    }
}

internal class Foo;
public class Bar : Foo;

internal class Foo;
public class Bar : Foo;