On https://portableapps.com/apps/development/swi-prolog_portable, it is stated:
System Requirements: Windows XP/Vista/7/8/10
License: Free / Open Source (SWI-Prolog: GPL/LGPL, Launcher: GPL)
Since some versions, the oldest Windows release supported is AFAIK, Windows 7. Since 7.4.x, the license was changed to BSD 2-clause. You can checkout http://www.swi-prolog.org to verify these claims.
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I've confirmed both of those.
The application page has been updated, although the application itself has not yet been updated to require Windows 7 or higher - this will be fixed in an upcoming release.
As the page has been updated, we're good closing this as a 'bug' though it's more of a documentation change. We'll have SWI check for Win7 on next release. A launcher not checking isn't really a bug, though, as it's not a requirement. More of a convenience.
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