# What fonts are used in this formula?

I have been trying to match the following style for some work I am doing but can't see to match the various font weights very well. Does anyone know which fonts are being used?

In particular I can't seem to get the curly l, the 5 pointed asterisk and the right kerning between the fn and x.

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You can get the "curly l" by typing \ell. – user15497 Jun 11 '12 at 3:47

That's Helvetica and Courier - probably from using a Times font package \usepackage{mathptmx} (they tend to pull Helvetica and Courier for sans serif and monospaced text). The curly "C" looks like a usual \mathcal. The double brackets are probably from stmaryrd.sty and are called \llbracket and \rrbracket. The star is \star. And the curly l is \ell.
The kerning between fn and "x" is probably obtained by \mathop{\mathtt{fn}}x – egreg Mar 16 '12 at 23:14