var map3 = new Dictionary<Func<int, bool>, int>();
    map3.Add((x) => x % 2 == 0, 1);
    map3.Add((x) => x % 10 == 0, 2);
    // ...

    var key = map3.Keys.SingleOrDefault(f => f(2));
    // key = (x) => x % 2
    // map3[key] = 1

Func<int, int> f = x => x*x + 1;
        Func<int, int> g = x => x*x + 1;
        Console.WriteLine(f.Equals(g)); // prints False

var map3 = new List<Tuple<Func<int,bool>,int>> {
    new Tuple<Func<int,bool>,int>((x) => x % 2 == 0, 1)
,   new Tuple<Func<int,bool>,int>((x) => x % 10 == 0, 2)
};
var t = map3.SingleOrDefault(t => t.Item1(2));
if (t != null) {
    var v = t.Item2;
}

void Main()
{
    var map3 = new List<(Func<int, bool> Key, int Value)> {
        ((x) => x * 2 == 4, 1),
        ((x) => x * 10 == 100, 2)
    };

    var result = map3.SingleOrDefault(x => x.Item1(10));
    Console.WriteLine(result.Value);
}