+1=1 became false between versions 8.5.5 and 8.5.10. How and why?

Alternatively, go to the download page (SWI-Prolog downloads) and follow the ChangeLog link. That gives a page with the latest release changelog and a menu that allows selecting a range of versions. Select 8.5.5 and 8.5.10 and search for + and you find

[Jan 26 2022]

MODIFIED: Read +digits as a term rather than a number. This changes also removes the space when writing e.g. +42. Reading +digits as a number predates the ISO standard and current practice. It was in SWI-Prolog since version 2.5 …

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