-@samp{caught WARNING: Result is a SYMBOL, not a NUMBER.} This is the
-@dfn{explanation} of the problem. In this example, the problem is that
-@code{y} evaluates to a symbol, but is in a context where a number is
-required (the argument to @code{+}).
+@samp{caught WARNING: Asserted type NUMBER conflicts with derived type
+(VALUES SYMBOL &OPTIONAL).} This is the @dfn{explanation} of the
+problem. In this example, the problem is that, while the call to
+@code{+} requires that its arguments are all of type @code{number},
+the compiler has derived that @code{y} will evaluate to a
+@code{symbol}. Note that @samp{(VALUES SYMBOL &OPTIONAL)} expresses
+that @code{y} evaluates to precisely one value.