difference between iqueryable and ienumerable

here

question on delegate predicates

in the following class:

class testLinq

    {

       

        public  bool www(string s)

        { return s.Equals("def"); }

        public delegate bool d(string s);

        public void write()

        {

           

            List<String> l = new List<string>() { "abc", "def" };

             

            normal way of doing predicate:  

            Console.WriteLine(l.Find(p => { return p.Equals("def"); }));

            

            bizzare method: 

            Predicate<string> pred = new Predicate<string>(www); 

            Console.WriteLine(l.Find(pred));

            non working method - 

            d di = null;

            di  = www;

            Console.WriteLine(l.Find(di)));

         Why?

            

            Console.ReadLine();

        }

    }

words that c# compiler add to LINQ

for example:
in this case

SortedList<int, string> sl = new SortedList<int, string>() { { 4, "beatrice" }, { 2, "herby" } };

this 

Console.WriteLine(sl.FirstOrDefault((KeyValuePair<int, string> p) => {return p.Key == 4; }).Value);

is equivelant to this:

Console.WriteLine(sl.FirstOrDefault(p => p.Key == 4).Value);

var in c#

why does c# have a var keyword ?
if you answer because of linq- that would be partly correct
consider:

Type t = this.GetType();

PropertyInfo[] p = t.GetProperties();

var names = from nms in p select nms.Name;

in this case the var is not necessary

the following could be written

We need var in a case where we are using implicitly typed local variables:

this.listBox1.Items.Clear();

            Type t = this.GetType();

            PropertyInfo[] p = t.GetProperties();

            var names = from nms in p select new {Name = nms.Name,Typ =nms.PropertyType};

            foreach (var s in names)

            {

                this.listBox1.Items.Add(s.Name +" "+ s.Typ.ToString());  

            }

IEnumerable<string> names = from nms in p select nms.Name;