Explore and Focus can be used separately, but used together have some great synergy effects. 

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Knowing that Focus will follow Explore allows you to freely do broad explorations. 

Planning to use the Focus tool allows you to build a lot more maps in the Explore tool. Building 15-20 maps will give you several hundred papers, and knowing you will iterate the list down easily later means you do not have to review every map content in detail. 
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The visual overview from Explore gives you a head start when Focusing. 

Having first used the Explore tool to find papers to then iterate down the list in the Focus tool, means you have had a visual overview of all important concepts in the papers. This gives you a clear advantage when picking concepts for inclusion/exclusion in Stage 1, as you know very well what is in your document set. 

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