Worth remembering that, on this date, 9 years ago, WG17 changed the course of Prolog standardization:
I like the yfy-fixish operator. I use something similar in one of my projects to distinguish between a + b + c and a - b - c.
yfy means “don’t care”. For example, +. Then a term like a + (b + c) is actually rendered as a + b + c.