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c# Find an item in 2 / multiple lists
private static IEnumerable<TSource> ConcatIterator<TSource>(IEnumerable<TSource> first, IEnumerable<TSource> second)
{
    foreach (TSource iteratorVariable0 in first)
    {
        yield return iteratorVariable0;
    }
    foreach (TSource iteratorVariable1 in second)
    {
        yield return iteratorVariable1;
    }
}

IEnumerable<string> concatenated = new[] { firstColl, secondColl }
    .SelectMany(item => item);

var query = list1.Concat(list2).Where(x => x.Category=="my category");

var matched = list1.Concat(list2).FirstOrDefault(e => element.Equals(e));

BaseType matched = list1.Concat(list2).Concat(list3).FirstOrDefault(e => element.Equals(e));

var list1 = new List<int>{1,2,3,4,5,6,7};
var list2 = new List<int>{0,-3,-4,2};

int elementToPush = 4;//value to find among available lists

var exist = list1.Exists(i=>i==elementToPush) || list2.Exists(j=>j==elementToPush);

List<string> a = new List<string>{"apple", "aardvark"};
List<string> b = new List<string>{"banana", "bananananana", "bat"};
List<string> c = new List<string>{"cat", "canary"};
List<string> d = new List<string>{"dog", "decision"};

List<List<string>> super = new List<List<string>> {a,b,c,d};

super.Any(x=>x.Contains("apple"));