Did it with .NET - A Higher Calling (revisited)
… already have equivalents in the .NET Framework 3.5.
1. Filter = Where
2. Map = Select
3. Reduce = Aggregate
Each of these are implemented as extension methods for IEnumerable. So, we can rewrite the code like this:

static void Main()
{

var numbers = new int[] { 1, 2, 3, 4, 5, [...]