Possible Duplicate:
Separate labels in cases
I want to label each equation in a collection of equations as in the example below. How can I do this?

Possible Duplicate:
Separate labels in cases
I want to label each equation in a collection of equations as in the example below. How can I do this?

Just use \eqref{eq:first}-\eqref{eq:last} if you are using the amsmath package and (\ref{eq:first})-(\ref{eq:last}) if you do not use it.
casesenvironment, with each line numbered. I'm still not sure what the question is asking, though. – Andrew Uzzell Oct 22 '12 at 14:55casesenvironment. Could you just refer to lines 1, 2, or 3 of the (single) equation rendered as acasesenvironment? – Mico Oct 22 '12 at 15:12subnumcaseswould be the answer. On the other hand, if you need to refer to all the lines, it's probably better to use only one number for the whole equation. After all, it's the definition of one function; what does (1) refer to? To "0", to "if x>0" or to both? – egreg Oct 22 '12 at 15:27