Minor grammatical fix.
diff --git a/Doc/lib/compiler.tex b/Doc/lib/compiler.tex
index 0c7c06d..d75dad7 100644
--- a/Doc/lib/compiler.tex
+++ b/Doc/lib/compiler.tex
@@ -89,7 +89,7 @@
phases. One set of errors is detected by the interpreter's parser,
the other set by the compiler. The compiler package relies on the
interpreter's parser, so it get the first phases of error checking for
-free. It implements the second phase itself, and that implement is
+free. It implements the second phase itself, and that implementation is
incomplete. For example, the compiler package does not raise an error
if a name appears more than once in an argument list:
\code{def f(x, x): ...}