Enumerate equations in an array after a curly brace

Question

How to enumerate two equations that go after a curly brace? How to make the enumeration use digits and letters, so two equations have number 1.a and 1.b?

\documentclass{article}

\usepackage{amsmath}                                                            

\begin{document}
   \begin{equation}
        A \Rightarrow 
        \left\{\begin{array}{ll}
                    B_1, \text{ or}\\
                    B_2 
        \end{array}
        \right.
   \end{equation}
\end{document}

Like this http://tex.stackexchange.com/questions/78043/nested-equations-numbering ? — percusse, Feb 14 '15 at 00:06
The same post, but linked to the @egreg answer http://tex.stackexchange.com/a/78050/14757 — Sigur, Feb 14 '15 at 00:09

score 7 · Accepted Answer · answered Feb 14 '15 at 00:37

empheq provides the bracing, while subequations (from amsmath) provides the proper numbering:

enter image description here

\documentclass{article}

\usepackage{amsmath,empheq}

\begin{document}
\begin{subequations}
  \begin{empheq}[left=A\Rightarrow\empheqlbrace]{align}
    & B_1, \text{ or} \\
    & B_2 
  \end{empheq}
\end{subequations}
\end{document}

score 5 · Answer 2 · answered Feb 14 '15 at 00:34

cases provides subnumcases (also numcases, see documentation for details) for this.

\documentclass{article}

\usepackage{amsmath}
\usepackage{cases}

\begin{document}
        \begin{subnumcases}{A \Rightarrow}
                    B_1, &  or\\
                    B_2 &
        \end{subnumcases}
\end{document}

enter image description here

score 0 · Answer 3 · answered Feb 14 '15 at 00:31

I found package empheq which is really nice. This example is without a curly brace.

\documentclass{article}

\usepackage{amsmath}
\usepackage{empheq}

\begin{document}
   \begin{empheq}[left=A\Rightarrow]{align}
        &B1\\
        &B2
   \end{empheq}                                                                 
\end{document}

Edit: I do not how to make enumeration to be 1.a, 1.b though.

Enumerate equations in an array after a curly brace

3 Answers3