How to write linq function query

Question

IRun<string, bool> runstub = c => One(1) == true;
exec(runstub);

What's wrong here? It gives an exception "Cannot convert lambda expression to type 'IRun' because it is not a delegate type"

public static IEnumerable<IStub> exec<T, M>(T t) where T : IRun<T, M>
{
}

public static bool One(int one)
{
    one.Dump();
    return 1;
}