For high gravity brews, more yeast is a good idea. If you want to use liquid yeast, make a starter.
You could use a dry and a liquid yeast, but the dry yeast will (most likely) have more yeast cells and dominate the ferment.
Remember one unassailable statistic, as explained by the late, great George Carlin: "Just think of how stupid the average person is, and then realize half of them are even stupider!"
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