  Working in a variant of the intersection type assignment system of Coppo,
Dezani-Ciancaglini and Veneri [1981], we prove several facts about sets of
terms having a given intersection type. Our main result is that every strongly
normalizing term $M$ admits a *uniqueness typing*, which is a pair $(\Gamma,A)$
such that
  1) $\Gamma \vdash M : A$
  2) $\Gamma \vdash N : A \Longrightarrow M =_{\beta\eta} N$
  We also discuss several presentations of intersection type algebras, and the
corresponding choices of type assignment rules.
