using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

public class Test
{
	public static void Main()
	{
        var researchTin = new Research  { Name = "Tin" };
        var researchFire = new Research  { Name = "Fire" };
        var researchWater = new Research  { Name = "Water" };
        var researchIron = new Research  { Name = "Iron" };
        var researchSteam = new Research  { Name = "Steam" };
        
        Dictionary<Research, List<Research>> requiredResearches = 
            new Dictionary<Research, List<Research>>();
    
        var req = new Research[] { researchTin };
        requiredResearches.Add(researchIron, req.ToList());
        
        req = new Research[] { researchFire, researchWater, researchIron };
        requiredResearches.Add(researchSteam, req.ToList());
        
        
        var playerResearches = new List<Research>();
        playerResearches.Add(researchFire);
        //playerResearches.Add(researchWater);
        //playerResearches.Add(researchTin);
        
        var chain = GetReq(requiredResearches, researchSteam);
       
        var missing = chain.Where (c => playerResearches.Where (r => r == c).Any () == false).Distinct();
        foreach(var miss in missing)
        {
            Console.WriteLine(miss.Name);
        }
    }

    public static IList<Research> GetReq(Dictionary<Research, List<Research>> reqs, Research target)
    {
        var chain = new List<Research>();
        if(reqs.ContainsKey(target))
        {
            foreach(var item in reqs[target])
            {
                chain.Add(item);
                chain.AddRange(GetReq(reqs, item));
            }
        }
        return chain;
    }
}

public class Element
{
}

public class Research
{
    public string Name { get; set; }
}