ClassicalFacts: adds a proof that weak excluded middle implies weak proof irrelevance.
ClassicalFacts: adds a proof that weak excluded middle implies weak proof irrelevance.

Application of previous commit in Hurkens.v.
SkySkimmer/coq,gares/coq,Lionel-Rieg/coq,aspiwack/coq,ejgallego/coq,Zimmi48/coq,Ptival/coq,TOSPIO/coq,amintimany/coq,Lionel-Rieg/coq,mlasson/coq,barras/coq,gmalecha/coq,8l/coq,TheTypoMaster/coq,letouzey/coq-wip,jpdeplaix/coq,letouzey/coq-wip,herbelin/github-coq,ppedrot/coq,JasonGross/coq,8l/coq,pirapira/coq2rust,pirapira/coq2rust,coq/coq,coq/coq,mlasson/coq,JasonGross/coq,asr/coq,Zimmi48/coq,Ptival/coq,silene/coq,herbelin/github-coq,TOSPIO/coq,Matafou/coq,ale-f/coq,ale-f/coq,SkySkimmer/coq,letouzey/coq-wip,JasonGross/coq,jpdeplaix/coq,SkySkimmer/coq,ejgallego/coq,asr/coq,shindere/coq,gares/coq,mattam82/coq,gares/coq,Matafou/coq,ejgallego/coq,gmalecha/coq,TheTypoMaster/coq,ejgallego/coq,ale-f/coq,ppedrot/coq,asr/coq,aspiwack/coq,maximedenes/coq,william-lawvere/coq,shindere/coq,herbelin/github-coq,pirapira/coq2rust,mattam82/coq,shindere/coq,coq/coq,TheTypoMaster/coq,silene/coq,maximedenes/coq,mattam82/coq,SkySkimmer/coq,william-lawvere/coq,Ptival/coq,silene/coq,jpdeplaix/coq,Matafou/coq,coq/coq,TOSPIO/coq,maximedenes/coq,letouzey/coq-wip,Zimmi48/coq,letouzey/coq-wip,mlasson/coq,ppedrot/coq,gares/coq,maximedenes/coq,JasonGross/coq,barras/coq,ppedrot/coq,maximedenes/coq,ppedrot/coq,Zimmi48/coq,barras/coq,8l/coq,gmalecha/coq,william-lawvere/coq,gares/coq,Lionel-Rieg/coq,aspiwack/coq,amintimany/coq,amintimany/coq