Page Layout ⇒ Flushleft and flushright in margins (odd an even pages)?

[imajcena]

I'm writing a book and I am putting some images in the margin. I don't like the default position of the image in the margin. It should be flushed left on the odd pages and flushed right on the right pages, so I want it right next to the text.

There is a problem with the code below, it doesn't work if the environment just starts on the new page (see the attached file, the position of the first \bigoplus on page 2 should be the same as the position of the second!). How could I prevent that? Help is highly appreciated.
Btw, I have no other margin types so this could even be set as a general default for the margins, not only in "dokaz" environment.

Code: Select all

\documentclass[b5paper,11pt]{book}
\usepackage[frame,a4,center]{crop}
\usepackage[latin2]{inputenc}
\usepackage{amssymb}
\usepackage{lipsum}
\usepackage{ifthen}%the position depends on whether the page is odd or even

\newenvironment{dokaz}{\noindent{\sc Dokaz.{}} \marginpar{
\ifthenelse{\isodd{\thepage}}
{\flushleft$\bigoplus$}
{\flushright$\bigoplus$}
}}
{\hspace*{\fill}\nolinebreak[1]\hspace*{\fill}$\square$\vskip.3cm}

\begin{document}
\lipsum[1]

\begin{dokaz}
\lipsum[1-2]
\end{dokaz}

\begin{dokaz}
\lipsum[3]
\end{dokaz}

\begin{dokaz}
\lipsum[4]
\end{dokaz}

\end{document}

[imajcena]

Doesn't anyone know the answer to this? Or perhaps I wasn't clear about where the problem is?

[gmedina]

Doesn't anyone know the answer to this? Or perhaps I wasn't clear about where the problem is?

Yes, I know the answer, and no, you were clear enough.

The problem comes from the asynchronous way in which LaTeX builds pages; this means that, in your code, the condition of the iftenelse command is evaluated while a page is built, and later on LaTeX's routines decided to move the relevant part of text to the next page, producing undesired results.

This is a typical example to show that it's not a good idea to use simply \thepage when defining commands like yours.

The solution (also typical (see The LaTeX Companion, for example)) is to use a combination of \label and \pageref commands:

Code: Select all

\documentclass[b5paper,11pt]{book}
\usepackage[frame,a4,center]{crop}
\usepackage[latin2]{inputenc}
\usepackage{amssymb}
\usepackage{lipsum}
\usepackage{ifthen}%the position depends on whether the page is odd or even

\newcounter{pl}
\newenvironment{dokaz}
  {\noindent{\scshape Dokaz.{}}%
   \stepcounter{pl}\label{pl-\thepl}%
   \marginpar{%
     \ifthenelse{\isodd{\pageref{pl-\thepl}}}%
     {\flushleft$\bigoplus$}%
     {\flushright$\bigoplus$}}}
  {\hspace*{\fill}\nolinebreak[1]\hspace*{\fill}$\square$\vskip.3cm}

\begin{document}
\lipsum[1]

\begin{dokaz}
\lipsum[1-2]
\end{dokaz}

\begin{dokaz}
\lipsum[3]
\end{dokaz}

\begin{dokaz}
\lipsum[4]
\end{dokaz}

\lipsum[1]

\begin{dokaz}
\lipsum[1-2]
\end{dokaz}

\begin{dokaz}
\lipsum[3]
\end{dokaz}

\begin{dokaz}
\lipsum[4]
\end{dokaz}

\end{document}

[imajcena]

Thank you!