RA query to find the age of the oldest person (or people) who eat mushroom pizza. https://stanford.io/2GkWfPx

gistfile1.txt

(
    \project_{age}(
        \select_{pizza='mushroom'}(Person\join Eats)
    )
)
\diff  
(
    \project_{age1}
    (
    (
        \select_{age1 < age2}(
            (\rename_{age1}(
                \project_{age}(\select_{pizza='mushroom'}(Person\join Eats))
                )
            )
            \cross
            (\rename_{age2}(
                \project_{age}(\select_{pizza='mushroom'}(Person\join Eats))
                )
            )
        )
    )
    )
)