SUB>&nbsp;<TT>=</TT>&nbsp;<I>vid</I><SUB>2</SUB> </TD>
    <TD> <TT>constructor</TT>&nbsp;<I>vid</I><SUB>1</SUB>&nbsp;<TT>=</TT>&nbsp;<I>vid</I><SUB>2</SUB> </TD>
  </TR>
</TABLE>



<?php section("wildcards", "type wildcards") ?>

<P>Type annotations may contain underscores as unspecified subcomponents:</P>

<PRE class=code>
fun mapSnd (f : _ -> _ * _) l = List.map (#2 o f) l</PRE>

<P>Unlike type variables, type wildcards do not enforce polymorphic typing. They
are thus suitable to leave out any part of a