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Si vous voulez effacer vos output .Voici la méthode.
You can try do those following steps since it worked for me :
Select the "Cell" -> then select "All Outputs" -> There you will find "Clear" option select that.
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This will reduce the size of your file (From MBs to kbs). It will also reduce the time to load the notebook next time you open it in your browser.
As per my understanding this It will clear all the output created after execution of the code. Since Notebook is holding code+images+comments in addition to this its also holding the out put in that file therefore it will increase the size of the notebook.