procedure main()

a := set(["John", "Serena", "Bob", "Mary", "Serena"])
b := set(["Jim", "Mary", "John", "Jim", "Bob"])

showset("a",a)
showset("b",b)
showset("(a\\b) \xef (b\\a)",(a -- b) ++ (b -- a))
showset("(a\\b)",a -- b)
showset("(b\\a)",b -- a)
end


procedure showset(n,x)
writes(n," = { ")
every writes(!x," ")
write("}")
return
end