diff --git a/cd.sh b/cd.sh
index 8d3a52c..f049f04 100644
--- a/cd.sh
+++ b/cd.sh
@@ -44,7 +44,7 @@ local variable
     CD_PYTHON_COMMAND="python3"
     #
     case "${CD_OS_NAME}" in
-        "debian")
+        "${CD_OS_DEBIAN}")
             case "${CD_OS_VERSION}" in
                 "bookworm"|"bullseye") cd_nop ;;
                 *) cd_error_os "CD_OS_VERSION" ;;
@@ -53,7 +53,7 @@ local variable
             CD_PYTHON_PACKAGES="/usr/lib/python3/dist-packages"
             CD_CA_ROOT="/usr/local/share/ca-certificates"
         ;;
-        "alma")
+        "${CD_OS_ALMA}")
             case "${CD_OS_VERSION}" in
                 "8"|"9")
                     CD_PYTHON_PACKAGE="python3.11"
@@ -120,7 +120,7 @@ local expression
 local file
     cd_step "Set packages repositories"
     case "${CD_OS_NAME}" in
-        "debian")
+        "${CD_OS_DEBIAN}")
             cd_write "/etc/apt/sources.list" "\
 deb https://deb.debian.org/debian ${CD_OS_VERSION} main
 deb https://deb.debian.org/debian ${CD_OS_VERSION}-backports main
@@ -128,7 +128,7 @@ deb https://deb.debian.org/debian ${CD_OS_VERSION}-updates main
 deb https://deb.debian.org/debian-security ${CD_OS_VERSION}-security main
 "
         ;;
-        "alma")
+        "${CD_OS_ALMA}")
             file="/etc/yum.repos.d/almalinux.repo"
             cd_sed "${file}" "|^m|# m|" "|^# b|b|"
             cd_cat "${file}"
@@ -139,7 +139,7 @@ deb https://deb.debian.org/debian-security ${CD_OS_VERSION}-security main
 cd_set_packages_configuration () {
     cd_step "Set packages configuration"
     case "${CD_OS_NAME}" in
-        "debian")
+        "${CD_OS_DEBIAN}")
             export DEBIAN_FRONTEND="noninteractive"
             cd_write "/etc/apt/apt.conf.d/apt.conf" "\
 Acquire::Check-Valid-Until True;
@@ -149,7 +149,7 @@ APT::Install-Suggests False;
 Dir::Etc::SourceParts \"\";
 "
         ;;
-        "alma") cd_mkdir "/etc/dnf/dnf.conf.d" ;;
+        "${CD_OS_ALMA}") cd_mkdir "/etc/dnf/dnf.conf.d" ;;
     esac
 }
 
@@ -172,12 +172,12 @@ cd_set_https_verification_off () {
     if [ "${CD_CA}" ] ; then
         cd_step "Set HTTPS verification off"
         case "${CD_OS_NAME}" in
-            "debian")
+            "${CD_OS_DEBIAN}")
                 cd_write "/etc/apt/apt.conf.d/https" "\
 Acquire::https::Verify-Peer False;
 "
             ;;
-            "alma")
+            "${CD_OS_ALMA}")
                 cd_write "/etc/dnf/dnf.conf.d/https.conf" "\
 sslverify=False
 "
@@ -189,16 +189,16 @@ sslverify=False
 cd_update_packages_catalog () {
     cd_step "Update packages catalog"
     case "${CD_OS_NAME}" in
-        "debian") apt-get update || exit ;;
-        "alma") dnf makecache || exit ;;
+        "${CD_OS_DEBIAN}") apt-get update || exit ;;
+        "${CD_OS_ALMA}") dnf makecache || exit ;;
     esac
 }
 
 cd_install_packages_tools () {
     cd_step "Install packages tools"
     case "${CD_OS_NAME}" in
-        "debian") cd_install_package "apt-utils" ;;
-        "alma") echo "TODO" ;;
+        "${CD_OS_DEBIAN}") cd_install_package "apt-utils" ;;
+        "${CD_OS_ALMA}") echo "TODO" ;;
     esac
 }
 
@@ -210,8 +210,8 @@ cd_install_ca_certificates () {
 cd_update_ca_certificates () {
     cd_step "Update CA"
     case "${CD_OS_NAME}" in
-        "debian") update-ca-certificates || exit ;;
-        "alma") update-ca-trust || exit ;;
+        "${CD_OS_DEBIAN}") update-ca-certificates || exit ;;
+        "${CD_OS_ALMA}") update-ca-trust || exit ;;
     esac
 }
 
@@ -219,8 +219,8 @@ cd_set_https_verification_on () {
     if [ "${CD_CA}" ] ; then
         cd_step "Set HTTPS verification on"
         case "${CD_OS_NAME}" in
-            "debian") cd_rm "/etc/apt/apt.conf.d/https" ;;
-            "alma") cd_rm "/etc/dnf/dnf.conf.d/https.conf" ;;
+            "${CD_OS_DEBIAN}") cd_rm "/etc/apt/apt.conf.d/https" ;;
+            "${CD_OS_ALMA}") cd_rm "/etc/dnf/dnf.conf.d/https.conf" ;;
         esac
     fi
 }
@@ -228,8 +228,8 @@ cd_set_https_verification_on () {
 cd_upgrade_packages () {
     cd_step "Upgrade packages"
     case "${CD_OS_NAME}" in
-        "debian") apt-get upgrade --assume-yes || exit ;;
-        "alma") dnf upgrade --assumeyes || exit ;;
+        "${CD_OS_DEBIAN}") apt-get upgrade --assume-yes || exit ;;
+        "${CD_OS_ALMA}") dnf upgrade --assumeyes || exit ;;
     esac
 }
 
@@ -246,8 +246,8 @@ cd_install_python () {
 cd_clean_packages_cache () {
     cd_step "Clean packages cache"
     case "${CD_OS_NAME}" in
-        "debian") apt-get clean || exit ;;
-        "alma") dnf clean all || exit ;;
+        "${CD_OS_DEBIAN}") apt-get clean || exit ;;
+        "${CD_OS_ALMA}") dnf clean all || exit ;;
     esac
 }
 
@@ -328,8 +328,8 @@ local variable="${1}"
 cd_install_package () {
     if [ "${1}" ] ; then
         case "${CD_OS_NAME}" in
-            "debian") apt-get install --assume-yes "${1}" || exit ;;
-            "alma") dnf install --assumeyes "${1}" || exit ;;
+            "${CD_OS_DEBIAN}") apt-get install --assume-yes "${1}" || exit ;;
+            "${CD_OS_ALMA}") dnf install --assumeyes "${1}" || exit ;;
         esac
     fi
 }
@@ -388,5 +388,10 @@ local text="${2}"
     fi
 }
 
+# constants
+
+CD_OS_ALMA="alma"
+CD_OS_DEBIAN="debian"
+
 # run
 cd_main