Equation references

Instead of referring to pages, it's most useful if equation labels refer to equation numbers. Therefore, Eplain reserves a \count register, \eqnumber, for the current equation number, and increments it at each numbered equation.

Here are the commands to define equation labels and then refer to them:

\eqdef{label}

This defines label to be the current value of \eqnumber, and, if the current context is not inner, then produces a \eqno command. (The condition makes it possible to use \eqdef in an \eqalignno construction, for example.) The text of the equation number is produced using \eqprint. See section Formatting equation references. If label is empty, you still get an equation number (although naturally you can't reliably refer to it). This is useful if you want to put numbers on all equations in your document, and you don't want to think up unique labels.

\eqdefn{label}

This is like \eqdef, except it always omits the \eqno command. It can therefore be used in places where \eqdef can't; for example, in a non-displayed equation. The text of the equation number is not produced, so you can also use it in the (admittedly unusual) circumstance when you want to define an equation label but not print that label.

\eqref{label}

This produces a formatted reference to label. If label is undefined (perhaps because it is a forward reference), it just produces the text of the label itself. Otherwise, it calls \eqprint.

\eqrefn{label}

This produces the cross-reference text for label. That is, it is like \eqref, except it doesn't call \eqprint.

Equation labels can contain the same characters that are valid in general cross-references.

• Formatting equation references
• Subequation references