Notes
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 ∪ 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.