DEFINITION or4_ind()
TYPE =
       ∀P0:Prop
         .∀P1:Prop
           .∀P2:Prop
             .∀P3:Prop
               .∀P:Prop
                 .(P0→P)→(P1→P)→(P2→P)→(P3→P)→(or4 P0 P1 P2 P3)→P
BODY =
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