Math & Science ⇒ Why is the normal subgroup symbol called \lhd?

[aleph_aleph_null]

Sorry if this question belongs somewhere else; I'm new to this forum.

Most TeX symbols have fairly intuitive names, like \leq or \rightarrow. I always forget how to make left- or right-pointing triangles (as you might use for a normal subgroup, for instance) though, since "lhd' and "rhd" mean nothing to me. Does anybody know why these symbols were given these particular names (aside from the obvious "l = left" and "r = right" component)?

[Stefan Kottwitz]

Welcome to the forum!

Interesting question. Also I did not find an answer searching the various macro packages that define \lhd. I assume, once that name existed, others used it too.

Let's guess what \lhd and \rhd could mean.

• left hand drive, right hand drive ?
• left hand delta, right hand delta?

Left hand delta sounds good to me, since it looks like a delta turned to the left.

By the way, I would not phrase it the way that the normal subgroup symbol is called \lhd, but for the normal subgroup the symbol \lhd is used. But I know that was just meant for explanation. I phrased it that way to stress that symbol names are usually generic or by their look and shape, often not by function. So for my math papers that I write, I would define my own set of macros with name by function, such as \let\nsubgroup\lhd. So I never forget it and the code is more easier to read.

Stefan