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get_con_details (VanillaCon btys) = unionManyUniqSets (map get_bty btys)
get_con_details (InfixCon bty1 bty2) = unionUniqSets (get_bty bty1) (get_bty bty2)
-get_con_details (NewCon ty _) = get_ty ty
get_con_details (RecCon nbtys) = unionManyUniqSets (map (get_bty.snd) nbtys)
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