@multitable @columnfractions .33 .66
@item @code{@var{argN}}
-@tab @var{n}th argument
+@tab @var{n}th argument.
@item @code{@var{typeN?}}
-@tab a Scheme @emph{type predicate} for which @code{@var{argN}}
+@tab A Scheme @emph{type predicate} for which @code{@var{argN}}
must return @code{#t}. There is also a special form
@code{(@emph{predicate?} @emph{default})} for specifying optional
arguments. If the actual argument is missing when the function is being