If I write something like this:

var things = mythings
    .Where(x => x.IsSomeValue)
    .Where(y => y.IsSomeOtherValue)

Is this the same as:

var results1 = new List<Thing>();
foreach(var t in mythings)
    if(t.IsSomeValue)
        results1.Add(t);

var results2 = new List<Thing>();
foreach(var t in results1)
    if(t.IsSomeOtherValue)
        results2.Add(t);

Or is there some magic under the covers that works more like this:

var results = new List<Thing>();
foreach(var t in mythings)
    if(t.IsSomeValue && t.IsSomeOtherValue)
        results.Add(t);

Or is it something completely different altogether?