# what does this triangle-like notation mean?

$$\triangleright\quad \text{and}\quad \triangleleft$$

I saw these notations in some abstract algebra texts and i don't know what does this mean.

What do they mean?

• Fortunately in this case the context is narrow enough to take a guess. In general though, if you have a question about notation, give a line or two of context where it is used. After all, not all mathematical symbols have a fixed universal meaning in all contexts. – rschwieb Apr 14 '14 at 14:14