Ecco il codice compilabile:
`\documentclass [a4paper, oneside]{article}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage[italian]{babel}
\usepackage{microtype}
\usepackage{calc}
\usepackage{amsmath}
\begin{document}
\begin{alignat*}{5}
&\mathrm{Alimenti\Rightarrow[H^+]}\;+\; && \mathbf{HCO_3^-} && \Rightarrow && \;\mathrm{CO_2+H_20} && \text{ (polmone)}\\
& && \begin{minipage}{\widthof{$\mathbf{HCO_3^-}$}} \centering{$\Uparrow$} \end{minipage}&& \Leftarrow && && \text{ (rene)}.
\end{alignat*}
\end{document}`
Ricapitolando (al di là delle graffe eventualmente ridondanti):
1) \centering{$\Uparrow$} —> compilazione ok, freccia centrata
2) {\centering $\Uparrow$} —> compilazione ok, freccia non centrata
3) {\centering $\Uparrow$\par} —> compilazione errata
Di seguito l’errore che viene fuori con (3):
“! Paragraph ended before \alignat* was complete.
\par
l.13 …hbf{HCO_3^-}$}} {\centering $\Uparrow$\par
} \end{minipage}&& \Leftar…
I suspect you’ve forgotten a `}’, causing me to apply this
control sequence to too much text. How can we recover?
My plan is to forget the whole thing and hope for the best.
! Missing $ inserted.
$
l.13 …hbf{HCO_3^-}$}} {\centering $\Uparrow$\par
} \end{minipage}&& \Leftar…
I’ve inserted a begin-math/end-math symbol since I think
you left one out. Proceed, with fingers crossed.
! Missing \endgroup inserted.
\endgroup
l.13 …hbf{HCO_3^-}$}} {\centering $\Uparrow$\par
} \end{minipage}&& \Leftar…
I’ve inserted something that you may have forgotten.
(See the
With luck, this will get me unwedged. But if you
really didn’t forget anything, try typing `2′ now; then
my insertion and my current dilemma will both disappear.
! Display math should end with $$.
\par
l.13 …hbf{HCO_3^-}$}} {\centering $\Uparrow$\par
} \end{minipage}&& \Leftar…
The `$’ that I just saw supposedly matches a previous `$$’.
So I shall assume that you typed `$$’ both times.
! Extra }, or forgotten \endgroup.
l.13 …bf{HCO_3^-}$}} {\centering $\Uparrow$\par}
\end{minipage}&& \Leftarr…
I’ve deleted a group-closing symbol because it seems to be
spurious, as in `$x}$’. But perhaps the } is legitimate and
you forgot something else, as in `\hbox{$x}’. In such cases
the way to recover is to insert both the forgotten and the
deleted material, e.g., by typing `I$}’.
! You can’t use `\unskip’ in vertical mode.
\endminipage ->\par \unskip
\ifvoid \@mpfootins \else \vskip \skip \@mpfooti…
l.13 …{\centering $\Uparrow$\par} \end{minipage}
&& \Leftarrow && …
Sorry…I usually can’t take things from the current page.
Try `I\vskip-\lastskip’ instead.
! Extra }, or forgotten \endgroup.
\endminipage …pagefalse \color@endgroup \egroup
\expandafter \@iiiparbox \…
l.13 …{\centering $\Uparrow$\par} \end{minipage}
&& \Leftarrow && …
I’ve deleted a group-closing symbol because it seems to be
spurious, as in `$x}$’. But perhaps the } is legitimate and
you forgot something else, as in `\hbox{$x}’. In such cases
the way to recover is to insert both the forgotten and the
deleted material, e.g., by typing `I$}’.
! Undefined control sequence.
\endminipage …\expandafter \@iiiparbox \@mpargs
{\unvbox \@tempboxa }
l.13 …{\centering $\Uparrow$\par} \end{minipage}
&& \Leftarrow && …
The control sequence at the end of the top line
of your error message was never \def’ed. If you have
misspelled it (e.g., `\hobx’), type `I’ and the correct
spelling (e.g., `I\hbox’). Otherwise just continue,
and I’ll forget about whatever was undefined.
)
Runaway argument?
\@checkend {minipage}\expandafter \endgroup \if@endpe \@doendpe \fi \if@ignore
\ETC.
! File ended while scanning use of \@iiiparbox.
\par
<*> prova.tex
I suspect you have forgotten a `}’, causing me
to read past where you wanted me to stop.
I’ll try to recover; but if the error is serious,
you’d better type `E’ or `X’ now and fix your file.
! Emergency stop.
<*> prova.tex
*** (job aborted, no legal \end found)
Here is how much of TeX’s memory you used:
3131 strings out of 493921
44747 string characters out of 3147282
132482 words of memory out of 3000000
6429 multiletter control sequences out of 15000+200000
5075 words of font info for 21 fonts, out of 3000000 for 9000
841 hyphenation exceptions out of 8191
30i,2n,35p,205b,106s stack positions out of 5000i,500n,10000p,200000b,50000s
! ==> Fatal error occurred, no output PDF file produced!”
Ciao!