one interface implementing another

I want to have the two interfaces below.

public interface IWriteable<T>
                where T : class
{
    void Add(T newEntity);
    void Remove(T entity);
}

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public interface IReadable<T>
            where T : class
{
    IQueryable<T> FindAll();
    IQueryable<T> FindWhere(Expression<Func<T, bool>> predicate);
    T FindById(int id);
    T FindById(Guid id);
}

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Basically I want to control certain elements of different aspects of my website.

So some repositories will only be able to read certain classes, some read/write.

What I want though is for IWriteable to also Implement IReadable as my attitude is if something has the permission to write it is ok to read.

Using my interface above how to I make Iwritebale implement IReadabale?