Performance of this operation

Is this a O(n^2) operation, or does it work like Hashsets in O(n).

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#### Document Details

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* ID: a5fb66fb-9a33-2550-2783-7ce2a4760219
* Version Independent ID: 2e80b927-7888-1fc8-7db9-d052b33ac87a
* Content: [Enumerable.Except Method (System.Linq)](https://docs.microsoft.com/en-us/dotnet/api/system.linq.enumerable.except?f1url=https%3A%2F%2Fmsdn.microsoft.com%2Fquery%2Fdev15.query%3FappId%3DDev15IDEF1%26l%3DEN-US%26k%3Dk(System.Linq.Enumerable.Except%60%601);k(TargetFrameworkMoniker-.NETFramework,Version%3Dv4.7.2);k(DevLang-csharp)%26rd%3Dtrue&view=netframework-4.7.2)
* Content Source: [xml/System.Linq/Enumerable.xml](https://github.com/dotnet/dotnet-api-docs/blob/master/xml/System.Linq/Enumerable.xml)
* Product: **dotnet-api**
* GitHub Login: @dotnet-bot
* Microsoft Alias: **dotnetcontent**