adam@10: fun mem [a ::: Type] [ns ::: {Unit}] (_ : eq a) (fl : folder ns) (x : a) (r : $(mapU a ns)) : bool =
adam@10:     @foldUR [a] [fn _ => bool]
adam@10:      (fn [nm ::_] [r ::_] [[nm] ~ r] y acc =>
adam@10:          acc || x = y)
adam@10:      False fl r