Add a notation for the empty type.
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ejgallego/coq,gares/coq,coq/coq,gares/coq,SkySkimmer/coq,SkySkimmer/coq,JasonGross/coq,silene/coq,gares/coq,coq/coq,Zimmi48/coq,silene/coq,Matafou/coq,Zimmi48/coq,gares/coq,JasonGross/coq,ejgallego/coq,coq/coq,JasonGross/coq,Matafou/coq,silene/coq,Zimmi48/coq,SkySkimmer/coq,ejgallego/coq,Zimmi48/coq,Matafou/coq,coq/coq,gares/coq,ejgallego/coq,JasonGross/coq,SkySkimmer/coq