Question: How to use Linq to find an item in a List of ProductCat where every ProductCat contains a List of Product.

I want to find the Product by ProductID.

Thanks

Answer: 
```
Product foundProduct = productCatList
            .SelectMany(list => list.Products)
            .Where(product => product.ProductID == whateverID)
            .SingleOrDefault()
```
For a pure Linq language syntax:

```
  var pds = from pc in prodCats
            select from p in pc.Products where p.ProductID < 3
            select p;

```

But I think the IEnumerable extension + lambda version is more readable.