doc: fix transitive closure example

diff --git a/doc/implementation.tex b/doc/implementation.tex
index 87d8e58..338ec07 100644 (file)
--- a/doc/implementation.tex
+++ b/doc/implementation.tex
@@ -548,7 +548,9 @@ $$
 R_1 \cup R_2
 \right)^+
 =
-R_2^+ \circ R_1^+
+\left(R_2^+ \circ R_1^+\right)
+\cup R_1^+
+\cup R_2^+
 .
 $$
 \end{example}