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I'm a new D&D 5e player and I'm making a character using both the players handbook and the new Mordenkainen’s Tome of Foes book. I was wanting to create a Githyanki Fighter.
I noticed that the fighter class give proficiency to all simple and martial weapons and all armor, while the githyanki race feature "Martial Prodigy" has proficient with light and medium armor and with shortswords, longswords, and greatswords.
Do I double the proficiency of these weapons and armors or what exactly would happen in this case? Do they stack somehow or are they redundant?