Alinear dentro de alinear

Question

Tengo que escribir ecuaciones en este formato:

    (1) A  → (*some terms*)
                   A.a = (*some terms*)
                   A.b = (*some terms*)
                   ...
                   A.z = (*some terms*)

    (2) B  → (*some terms*)
                   B.a = (*some terms*)
                   B.b = (*some terms*)
                   ...
                   B.z = (*some terms*)

    ...

    (5) E  → (*some terms*)
                   E.a = (*some terms*)
                   E.b = (*some terms*)
                   ...
                   E.z = (*some terms*)

Los números ((1), (2), etc.) deben estar a la izquierda, el símbolo '→' debe estar alineado y todos los símbolos '=' deben estar alineados. Además, Aa, Ab, etc. deben comenzar a la derecha de '→'.

¿Cómo puedo hacer esto? Soy un principiante en LateX.

Answer 1

Puede utilizar flalign; con \lefteqnel ancho del argumento se ignora.

\documentclass{article}
\usepackage{amsmath}

\begin{document}

Some text before the display just to see where the margins of the type block
are, some more to be sure
\begin{flalign*}
(1)\quad A &\to \lefteqn{(*some terms*)} &&& \\
& & A.a &= (*some terms*) \\
& & A.b &= (*some terms*) \\
& & A.c &= (*some terms*) \\
(2)\quad B &\to \lefteqn{(*some terms*)} \\
& & B.a &= (*some terms*) \\
& & B.b &= (*some terms*) \\
& & B.c &= (*some terms*) \\
(3)\quad C &\to \lefteqn{(*some terms*)} \\
& & C.a &= (*some terms*) \\
& & C.b &= (*some terms*) \\
& & C.c &= (*some terms*)
\end{flalign*}
Some text before the display just to see where the margins of the type block
are, some more to be sure

\end{document}

Answer 2

Siempre puede usar las capacidades de eqparboxpara proporcionar anchos de tamaño similar en los elementos del documento (como enumerateo align):

\documentclass{article}

\usepackage{amsmath,eqparbox,enumitem}

\begin{document}

Some text before the display just to see where the margins of the type block
are, some more to be sure:
\begin{enumerate}[label={(\arabic*)}]
  \item
  $\eqmakebox[LHSitem][r]{$A$} \to text{(*some terms*)}$
  \begin{align*}
    \eqmakebox[LHS][r]{$A.a$} &= \text{(*some terms*)} \\
    \eqmakebox[LHS][r]{$A.b$} &= \text{(*some terms*)} \\
    \eqmakebox[LHS][r]{$A.c$} &= \text{(*some terms*)}
  \end{align*}
  
  \item
  $\eqmakebox[LHSitem][r]{$AB$} \to \text{(*some terms*)}$
  \begin{align*}
    \eqmakebox[LHS][r]{$AB.a$} &= \text{(*some terms*)} \\
    \eqmakebox[LHS][r]{$AB.b$} &= \text{(*some terms*)} \\
    \eqmakebox[LHS][r]{$AB.c$} &= \text{(*some terms*)}
  \end{align*}
  
  \item
  $\eqmakebox[LHSitem][r]{$ABC$} \to \text{(*some terms*)}$
  \begin{align*}
    \eqmakebox[LHS][r]{$ABC.a$} &= \text{(*some terms*)} \\
    \eqmakebox[LHS][r]{$ABC.b$} &= \text{(*some terms*)} \\
    \eqmakebox[LHS][r]{$ABC.c$} &= \text{(*some terms*)}
  \end{align*}
\end{enumerate}
Some text before the display just to see where the margins of the type block
are, some more to be sure.

\end{document}