(imported comment written by SystemAdmin)
Here is a much more complicated example, that checks for the presence of a specific file, the LAME MP3 DLL, in the Audacity Install folder. This relevance does not assume Audacity is installed in a particular location, but gets the install location from the registry.
(not exists file (value
"InstallLocation" of keys whose (value
"DisplayName" of it as string as lowercase contains
"Audacity 1.3" as lowercase) of key
"HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall" of registry as string &
"Plug-Ins\lame_enc.dll")) OR (not(((380928 = size of it AND
"Fri, 28 Nov 2008 08:32:56 -0400" as time = modification time of it AND
"755b6e39607e45eeb3780a18edab580e9d2be4af" = sha1 of it) of file (value
"InstallLocation" of keys whose (value
"DisplayName" of it as string as lowercase contains
"Audacity 1.3" as lowercase) of key
"HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall" of registry as string &
"Plug-Ins\lame_enc.dll"))))​