TITLE: In what context are these mathematical symbols used?
QUESTION [11 upvotes]: I just noticed that the Unicode character set contains an entire block (256 characters) of math symbols. I've got no idea how some of them should be used. For example:

U+22DA (⋚) and U+22DB (⋛): less-than-equal-to-or-greater-than, and greater-than-equal-to-or-less-than. Why not just use the good old equals sign = ?
U+2295 through U+2298 (⊕⊖⊗⊘): circled + − × ⁄ symbols
U+2235 (∿): sine wave; why do we need a character for this? does anyone use this?
U+2268 (≨): less-than-but-not-equal-to; isn't this redundant? if x < y then isn't it always true the x ≠ y?

I got these from here (you can click "more").
Thanks!

REPLY [11 votes]: $⋚$ and $⋛$ seem appropriate for use with partial orderings; i.e. $a⋚b$ would mean that $a$ and $b$ are comparable ($a⊥b$ is another convention for symbolising comparability).