diff --git a/CHANGES.md b/CHANGES.md
index 9b7ec5b9..fbf3c037 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -11,6 +11,8 @@ Documentation:
 
 - Add slides from the defense of projects MUNI/33/1654/2022 and
   MUNI/33/1658/2022 to `README.md`. (49f01ccf)
+- Remove `<mroot>` from MathML in the user manual. (#420, #422,
+  contributed by @quark67)
 
 Contributed Software:
 
diff --git a/Dockerfile b/Dockerfile
index 60979ea1..57b8a20f 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -23,6 +23,7 @@ ARG DEPENDENCIES="\
     poppler-utils \
     python3-pygments \
     python3-venv \
+    retry \
     ruby \
     unzip \
     wget \
@@ -66,19 +67,19 @@ set -o errexit
 set -o nounset
 set -o xtrace
 
+# Install dependencies
+apt-get -qy update
+apt-get -qy install --no-install-recommends ${DEPENDENCIES}
+
 # Update packages in non-historic TeX Live versions
 if echo ${TEXLIVE_TAG} | grep -q latest
 then
-  tlmgr update --self --all
+  retry -t 30 -d 60 tlmgr update --self --all
 elif echo ${TEXLIVE_TAG} | grep -q pretest
 then
-  tlmgr update --self --all --repository ftp://ftp.cstug.cz/pub/tex/local/tlpretest/
+  retry -t 30 -d 60 tlmgr update --self --all --repository ftp://ftp.cstug.cz/pub/tex/local/tlpretest/
 fi
 
-# Install dependencies
-apt-get -qy update
-apt-get -qy install --no-install-recommends ${DEPENDENCIES}
-
 # Generate the ConTeXt file database
 mtxrun --generate
 
@@ -150,13 +151,25 @@ set -o errexit
 set -o nounset
 set -o xtrace
 
+# Install dependencies, but this time we clean up after ourselves
+apt-get -qy update
+apt-get -qy install --no-install-recommends ${DEPENDENCIES}
+if [ ${DEV_IMAGE} = true ]
+then
+  apt-get -qy install --no-install-recommends ${DEV_DEPENDENCIES}
+fi
+apt-get -qy autoclean
+apt-get -qy clean
+apt-get -qy autoremove --purge
+rm -rfv ${AUXILIARY_FILES}
+
 # Update packages in non-historic TeX Live versions
 if echo ${TEXLIVE_TAG} | grep -q latest
 then
-  tlmgr update --self --all
+  retry -t 30 -d 60 tlmgr update --self --all
 elif echo ${TEXLIVE_TAG} | grep -q pretest
 then
-  tlmgr update --self --all --repository ftp://ftp.cstug.cz/pub/tex/local/tlpretest/
+  retry -t 30 -d 60 tlmgr update --self --all --repository ftp://ftp.cstug.cz/pub/tex/local/tlpretest/
 fi
 
 # Uninstall the distribution Markdown package
@@ -186,18 +199,6 @@ set -o xtrace
 # Make the markdown-cli script executable
 chmod +x ${BINARY_DIR}/markdown-cli
 
-# Install dependencies, but this time we clean up after ourselves
-apt-get -qy update
-apt-get -qy install --no-install-recommends ${DEPENDENCIES}
-if [ ${DEV_IMAGE} = true ]
-then
-  apt-get -qy install --no-install-recommends ${DEV_DEPENDENCIES}
-fi
-apt-get -qy autoclean
-apt-get -qy clean
-apt-get -qy autoremove --purge
-rm -rfv ${AUXILIARY_FILES}
-
 # Generate the ConTeXt file database
 mtxrun --generate
 
diff --git a/markdown.dtx b/markdown.dtx
index 7b6ceb45..0438cff2 100644
--- a/markdown.dtx
+++ b/markdown.dtx
@@ -1881,7 +1881,7 @@ following text:
 
 > \$\\sqrt{-1}\$ *equals* \$i\$.
 >
-> <math><mroot><msqrt><mo>−</mo><mn>1</mn></msqrt></mroot></math>
+> <math><msqrt><mo>−</mo><mn>1</mn></msqrt></math>
 > *equals*
 > <math><mi>i</mi></math>.
 
@@ -1924,7 +1924,7 @@ following text:
 
 > \$\\sqrt{-1}\$ *equals* \$i\$.
 >
-> <math><mroot><msqrt><mo>−</mo><mn>1</mn></msqrt></mroot></math>
+> <math><msqrt><mo>−</mo><mn>1</mn></msqrt></math>
 > *equals*
 > <math><mi>i</mi></math>.
 
@@ -1977,7 +1977,7 @@ following text:
 
 > \$\\sqrt{-1}\$ *equals* \$i\$.
 >
-> <math><mroot><msqrt><mo>−</mo><mn>1</mn></msqrt></mroot></math>
+> <math><msqrt><mo>−</mo><mn>1</mn></msqrt></math>
 > *equals*
 > <math><mi>i</mi></math>.
 
@@ -7157,7 +7157,7 @@ following text:
 
 > \$\\sqrt {-1}\$ *equals* \$i\$.
 >
-> <math><mroot><msqrt><mo>−</mo><mn>1</mn></msqrt></mroot></math>
+> <math><msqrt><mo>−</mo><mn>1</mn></msqrt></math>
 > *equals*
 > <math><mi>i</mi></math>.
 
@@ -7199,7 +7199,7 @@ following text:
 
 > \$\\sqrt {-1}\$ *equals* \$i\$.
 >
-> <math><mroot><msqrt><mo>−</mo><mn>1</mn></msqrt></mroot></math>
+> <math><msqrt><mo>−</mo><mn>1</mn></msqrt></math>
 > *equals*
 > <math><mi>i</mi></math>.
 
@@ -7231,7 +7231,7 @@ following text:
 
 > \$\\sqrt {-1}\$ *equals* \$i\$.
 >
-> <math><mroot><msqrt><mo>−</mo><mn>1</mn></msqrt></mroot></math>
+> <math><msqrt><mo>−</mo><mn>1</mn></msqrt></math>
 > *equals*
 > <math><mi>i</mi></math>.
 
@@ -7263,7 +7263,7 @@ following text:
 
 > \$\\sqrt {-1}\$ *equals* \$i\$.
 >
-> <math><mroot><msqrt><mo>−</mo><mn>1</mn></msqrt></mroot></math>
+> <math><msqrt><mo>−</mo><mn>1</mn></msqrt></math>
 > *equals*
 > <math><mi>i</mi></math>.
 
@@ -7295,7 +7295,7 @@ following text:
 
 > \$\\sqrt {-1}\$ *equals* \$i\$.
 >
-> <math><mroot><msqrt><mo>−</mo><mn>1</mn></msqrt></mroot></math>
+> <math><msqrt><mo>−</mo><mn>1</mn></msqrt></math>
 > *equals*
 > <math><mi>i</mi></math>.
 
@@ -11298,7 +11298,7 @@ following text:
 
 > \$\\sqrt{-1}\$ *equals* \$i\$.
 >
-> <math><mroot><msqrt><mo>−</mo><mn>1</mn></msqrt></mroot></math>
+> <math><msqrt><mo>−</mo><mn>1</mn></msqrt></math>
 > *equals*
 > <math><mi>i</mi></math>.
 
@@ -14083,7 +14083,7 @@ following text:
 >
 > \$\\sqrt{-1}\$ *equals* \$i\$.
 >
-> <math><mroot><msqrt><mo>−</mo><mn>1</mn></msqrt></mroot></math>
+> <math><msqrt><mo>−</mo><mn>1</mn></msqrt></math>
 > *equals*
 > <math><mi>i</mi></math>.
 
@@ -14124,7 +14124,7 @@ following text:
 >
 > \$\\sqrt{-1}\$ *equals* \$i\$.
 >
-> <math><mroot><msqrt><mo>−</mo><mn>1</mn></msqrt></mroot></math>
+> <math><msqrt><mo>−</mo><mn>1</mn></msqrt></math>
 > *equals*
 > <math><mi>i</mi></math>.
 
@@ -14161,7 +14161,7 @@ following text:
 >
 > \$\\sqrt{-1}\$ *equals* \$i\$.
 >
-> <math><mroot><msqrt><mo>−</mo><mn>1</mn></msqrt></mroot></math>
+> <math><msqrt><mo>−</mo><mn>1</mn></msqrt></math>
 > *equals*
 > <math><mi>i</mi></math>.
 
@@ -21053,7 +21053,7 @@ following text:
 
 > \$\\sqrt{-1}\$ *equals* \$i\$.
 >
-> <math><mroot><msqrt><mo>−</mo><mn>1</mn></msqrt></mroot></math>
+> <math><msqrt><mo>−</mo><mn>1</mn></msqrt></math>
 > *equals*
 > <math><mi>i</mi></math>.
 
@@ -21674,7 +21674,7 @@ following text:
 
 > \$\\sqrt{-1}\$ *equals* \$i\$.
 >
-> <math><mroot><msqrt><mo>−</mo><mn>1</mn></msqrt></mroot></math>
+> <math><msqrt><mo>−</mo><mn>1</mn></msqrt></math>
 > *equals*
 > <math><mi>i</mi></math>.