[defns.projection] Fix context to 'library'.

Author: jensmaurer

source/intro.tex

@@ -456,8 +456,9 @@
 
 \definition{projection}{defns.projection}
 \indexdefn{projection}%
-\defncontext{function object argument} transformation that
-an algorithm applies before inspecting the values of elements
+\defncontext{library}
+transformation that an algorithm applies
+before inspecting the values of elements
 
 \begin{example}
 \begin{codeblock}