public IEnumerable <Product> Filter(IEnumerable <Product> items, Ispecification <Product> spec)
{
foreach (var p in items)
{
if (spec.IsSatisfied(p))
{
yield return(p);
}
}
}
public bool IsSatisfied(T t)
{
return(first.IsSatisfied(t) && second.IsSatisfied(t));
}