using static System.Console;
using System.Collections.Generic;
using System.Linq;
 
string[] input = {
    "a1=a2", "b1=b2", "b3=b2", "c1=c2", "e1=e2", "a3=a4", "c3=c4", "e1=e3",
    "a2=a4", "c3=c1", "b3=a4", "c2=d1", "a4=a5", "d2=c1", "b4=b3", "d3=c3"
};
 
var a = new HashSet<string>();
var g = new List<HashSet<string>>();
 
foreach (var h in input.Select(s => s.Split('=').ToHashSet())) {
    a.UnionWith(h);
    var i = g.Select((x, i) => i).Where(i => g[i].Overlaps(h)).ToArray();
    switch (i.Length) {
        case 0: g.Add(h); break;
        case 1: g[i[0]].UnionWith(h); break;
        case 2: g[i[0]].UnionWith(g[i[1]]); g.RemoveAt(i[1]); break;
    }
}
 
g.ForEach(x => WriteLine($"[{string.Join(", ", a.Intersect(x))}]"));

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