Fred observes that the typo was not the only problem with this sentence.
diff --git a/Doc/ref/refa1.tex b/Doc/ref/refa1.tex
index b7b5acd..1074cfd 100644
--- a/Doc/ref/refa1.tex
+++ b/Doc/ref/refa1.tex
@@ -172,7 +172,7 @@
the binding of that name established in the innermost function block
containing the use.
-A \dfn{block} is a piece of Python program text that can is executed as
+A \dfn{block} is a piece of Python program text that is executed as
a unit. The following are blocks: a module, a function body, and a
class defintion.