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\documentclass[a4paper]{article}% librerie di lingua
\usepackage[italian]{babel}
\usepackage[latin1]{inputenc}
\usepackage[T1]{fontenc}\usepackage{pstricks}
\usepackage{pst-tree}
\usepackage{pst-plot}
\usepackage{pstricks-add}\usepackage{indentfirst}
\begin{document}
\end{document}
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Nessun problema con il tuo codice, a me compila perfettamente. Aggiungi \listfiles prima di \documentclass. Nel log dovresti ottenere un elenco dei file usati, come questo qui sotto:
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*File List*
article.cls 2005/09/16 v1.4f Standard LaTeX document class
size10.clo 2005/09/16 v1.4f Standard LaTeX file (size option)
babel.sty 2005/11/23 v3.8h The Babel package
italian.ldf 2005/11/17 v1.2r Italian support from the babel system
inputenc.sty 2006/05/05 v1.1b Input encoding file
latin1.def 2006/05/05 v1.1b Input encoding file
fontenc.sty
t1enc.def 2005/09/27 v1.99g Standard LaTeX file
pstricks.sty 2006/08/10 v0.32 LaTeX wrapper for `PSTricks' (RN,HV)
pstricks.tex 2006/12/22 v1.15 `PSTricks' (tvz)
xcolor.sty 2007/01/21 v2.11 LaTeX color extensions (UK)
color.cfg 2007/01/18 v1.5 color configuration of teTeX/TeXLive
dvips.def 1999/02/16 v3.0i Driver-dependant file (DPC,SPQR)
pst-tree.sty 2004/07/15 package wrapper for pst-tree.tex
pst-tree.tex 2004/07/24 97 patch 6 `pst-tree' (tvz)
pst-plot.sty 2004/07/15 package wrapper for pst-plot.tex
pst-plot.tex 2004/05/18 1.41 `pst-plot' (tvz)
pstricks-add.sty 2005/03/03 package wrapper for pstricks-add.tex (hv)
pstricks-add.tex 2006/11/22 v2.82 `PSTricks-add' (hv,dr)
pst-xkey.tex 2005/11/25 v1.6 PSTricks specialization of xkeyval (HA)
xkeyval.sty 2006/11/18 v2.5f package option processing (HA)
xkeyval.tex 2006/11/18 v2.5f key=value parser (HA)
indentfirst.sty 1995/11/23 v1.03 Indent first paragraph (DPC)
lgrcmr.fd 2001/01/30 v2.2e Greek Computer Modern
***********
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Riporta, per favore, il risultato che ottieni tu. Potrebbe trattarsi di un problema di file non aggiornati.
Ciao,
Max.