[type.descriptions.general] Use "shown" for impl-def types

Author: frederick-vs-ja

source/lib-intro.tex

@@ -561,7 +561,7 @@
 the library.
 
 \pnum
-Certain types defined in \ref{input.output} are used to describe implementation-defined types.
+Certain types shown in \ref{input.output} are used to describe implementation-defined types.
 \indextext{types!implementation-defined}%
 They are based on other types, but with added constraints.