Otared Kavian
The \triangle operator is used for instance in the « symmetric difference » of two subsets
Ah, good to learn something about pure mathematics. In my mathematics degree, my tutor said, "You are very good at the applied material," which was not meant as a compliment. So \triangle should be a \mathop rather than a \mathord? Right now, as Aditya pointed out, it's a \mathord ("ordinary"), in contrast to \bigtriangleup, which is the same character but typeset as a binary operator ("binary"). From char-def.lua : [0x25B3]={ adobename="whiteuppointingtriangle", category="so", cjkwd="a", description="WHITE UP-POINTING TRIANGLE", direction="on", linebreak="ai", mathspec={ { class="ordinary", name="triangle", }, { class="binary", name="bigtriangleup", }, }, unicodeslot=0x25B3, }, -Sanjoy