This online mathematical keyboard is limited to what can be achieved with Unicode characters. This means, for example, that you cannot put one symbol over another. While this is a serious limitation, multi-level formulas are not always needed and even when they are needed, proper math symbols still look better than improvised ASCII approximations.
Compare:
∀(x, y ∈ A ∪ B; x ≠ y) x² − y² ≥ 0
For all (x, y :- A u B; x != y) x^2 - y^2 >= 0
The advantage of using plain Unicode is that you can copy & paste your text into any text file, e-mail message or HTML document and it will (usually) be displayed correctly without any special plugins. If you need to type more complex mathematical formulas (e.g. fractions), you should use a more advanced tool like LaTeX.
This editor includes those Greek letters which are most commonly used in math, physics and other sciences. If you need to type other Greek letters, you can switch to the Greek keyboard while typing (your text will be preserved across editors)