MathTran uses TeX-notation for encoding mathematics. Most people use LaTeX, but for technical reasons MathTran uses a variant of the simpler plain TeX format.
The main difference between MathTran TeX and LaTeX is that MathTran doesn't use the LaTeX \begin{environment} and \end{environment} commands, and that it uses \hbox for text in a formula.
One the page Formulas | TeX you'll find links to many examples of how to use TeX.
Why not have a list of MathTran Tex commands. Am I expected to search through the formulas or try TeX commands to see whether or not they work?
$$\mathop {\lim }\limits_{x \to - \infty } f\left( x \right) = 1$$