This site requires a browser – like Firefox – which supports MathML.

Firemath - The Formula Editor

Example: Fences

If you have followed the foregoing examples, you should already be able to generate various elements. Therefore, the explanations here are less fine-grained.
You will find the set elements used in this example in the tabs panel under tabs and . With these you should be able to create expression

ℳ_{m}^{n} = \{x \in ℝ^{n}\}

Please make sure to use fences .
Fences are elements, which contain other elements. Separators between these elements can be specified individually. In this context, the fences in our example so far contain only one element. So how do we add a second element? Notice that Firemath shows two pink dots inside of the fences when in editing mode. If you locate the cursor on the dot on the right, you can start inserting the second element and make our expression look like

ℳ_{m}^{n} = \{x \in ℝ^{n}, x_{i} > 0\}

Obviously, the separators between the elements defaults to commas ','. This is not what we want in our case. Therefore, move the cursor until it covers the entire fences expression. Click the attributes button and insert '|,' (yes, two characters) behind 'Separators'.
Now, we are ready to insert the third element. Just make the equation appear as

ℳ_{m}^{n} = \{x \in ℝ^{n}| x_{i} > 0| {∥x∥}_{\infty} = m\}

Once again, you can use a fences button to obtain this. The reason why we inserted the two characters '|,' for the separators becomes obvious, now. Inserting more elements inside our fences, the last character — the comma in our case — is used as separator.
Into the bargain, also the fourth element contains fences. In fact, these fences contain three elements by themselves. An ellipsis button can be found in the tabs panel. Using this you reach our target: