Ciro Santilli @cirosantilli 35

Single chemical element, single phase (usually solid), but different 3D structures.

The prototypical examples are the allotropes of carbon such as diamond vs graphite.

Lower case looks like the mouth shape when you say Z, with mouth open, and you can even see the little tongue going down. Beauty.

This one is a little confusing: the upper case looks exactly like a letter P, but as the name suggests, it actually corresponds to the letter R. The letter P corresponds to pi instead.

One of the most nerve wrecking movies ever made. Until they decide to rescue their colleague from jail, then it just becomes too surreal.

The polynomials together with polynomial addition and multiplication form a commutative ring.

These are not in the Greek alphabet:

Basically a synonym of trope, but without the negative connotation.