Using 2 libraries with same namespace

Hello guys,

I've got a conflict between two libraries which have the same namespace. I added the Holotoolkit to my project, and it is using System.Threading(.Task) Version=4.0.10.0. I can't find this .dll in the project (so I can't do anything about it)

I also added the MathNet.Numerics dll, but it needs a System.Threading Version=1.0.2856.10 to run. So I've got both of them in a folder of my project.

This is an example of error :

Assets\Packages\HoloToolKitPackage\HoloToolkit\Input\Scripts\Utilities\MicrophoneHelper.cs(65,29): error CS0433: The type 'Task<TResult>' exists in both 'System.Threading.Tasks, Version=4.0.10.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' and 'System.Threading, Version=1.0.2856.102, Culture=neutral, PublicKeyToken=31bf3856ad364e35'

I found this : https://stackoverflow.com/a/37346836 , but I'm not using directly System.Threading, I only use MathNet.Numerics...

I've got no clue how to solve this, the rookie that I am would appreciate some help !

Unity 2018.1.0f2