C# field inheritance

interface ISomeInterface {}
class SomeInterfaceImpl : ISomeInterface {}

/* compilation error!
interface Base {
	ISomeInterface some { get; set; }
}
class ChildBase : Base {
	public SimeInterfaceImpl some { get; set; }
}
*/

interface Base<T> where T : ISomeInterface {
	T some { get; set; }
}
class ChildBase : Base<SomeInterfaceImpl> {
	public SomeInterfaceImpl some { get; set; }
}