unionmem=Marked_ororsetfalsenilMarked_memtruezyxor(true,y)trueor(x,true)trueor(false,false)falsemem(x,nil)falsemem(x,set(y))=(x,y)mem(x,union(y,z))or(mem(x,y),mem(x,z))or(true,y)trueor(x,true)trueor(false,false)falsemem(x,nil)falsemem(x,set(y))=(x,y)mem(x,union(y,z))or(mem(x,y),mem(x,z))Marked_mem(x,union(y,z))Marked_or(mem(x,y),mem(x,z))Marked_mem(x,union(y,z))Marked_mem(x,y)Marked_mem(x,union(y,z))Marked_mem(x,z)or(true,y)trueor(x,true)trueor(false,false)falsemem(x,nil)falsemem(x,set(y))=(x,y)mem(x,union(y,z))or(mem(x,y),mem(x,z))Marked_mem(x,union(y,z))Marked_mem(x,y)Marked_mem(x,union(y,z))Marked_mem(x,z)true0Marked_mem30nil0false0set330or0=20mem220union2330