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I'd like the arrow over f(P)f(Q) to be longer, without changing the default space between lines, if possible. Here's a minimal working example:

\documentclass[a4paper]{article}

\usepackage[T1]{fontenc}    
\usepackage[utf8]{inputenc}
\usepackage[italian]{babel}
\usepackage{fullpage}

\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{amsthm}
\usepackage{mathtools}

\newcommand{\pnt}[1]{\textsc{{#1}}}
\newcommand{\pntvec}[1]{\overset{\to}{\textsc{{#1}}}}

\begin{document}
    Siano $A$ uno spazio affine su $V$ e $A'$ uno spazio
    affine su $V'$. Un \emph{isomorfismo tra $A$ e $A'$} è
    un'applicazione $f \colon A \to A'$ tale che
    \[
    \exists \, \varphi \colon V \to V' \hspace{1.5mm}
    \textup{isomorfismo} \hspace{0.5mm} \mid \hspace{0.5mm}
    \overset{\longrightarrow}{f(\pnt{p})f(\pnt{q})} \, = \,
    \varphi(\pntvec{pq}) \quad \forall \, \pnt{p}, \pnt{q}
    \in A
    \]
    $\varphi$ si dice \emph{isomorfismo associato a $f$}.
\end{document}

enter image description here

2
  • 3
    Instead of \overset{\longrightarrow}{...} you probably want \overrightarrow{...}.
    – campa
    Oct 25, 2018 at 7:37
  • 1
    If you load mathtools, you do not need to \usepackage{amsmath} in your preamble.
    – Sebastiano
    Oct 25, 2018 at 20:12

1 Answer 1

5

As pointed in @campa's comment, you have the \overrightarrow command. I suggest loading old-arrowsto have smaller arrow tips,so the arrow tips do not touch the top of capital letters.

Another possibility is package esvect, which has 8 different arrow tips via an option. Here is a demo of both:

\documentclass[a4paper]{article}

\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage[italian]{babel}
\usepackage{fullpage}

\usepackage{old-arrows}
\usepackage[b]{esvect}
\usepackage{amssymb}
\usepackage{amsthm}
\usepackage{mathtools}

\newcommand{\pnt}[1]{\textsc{{#1}}}
\newcommand{\pntvec}[1]{\overrightarrow{\textsc{{#1}}}}

\begin{document}

    Siano $A$ uno spazio affine su $V$ e $A'$ uno spazio
    affine su $V'$. Un \emph{isomorfismo tra $A$ e $A'$} è
    un'applicazione $f \colon A \to A'$ tale che
    \[
    \exists \, \varphi \colon V \to V' \hspace{1.5mm}
    \textup{isomorfismo} \hspace{0.5mm} \mid \hspace{0.5mm}
    \overrightarrow{f(\pnt{p})f(\pnt{q})} \, = \,
    \varphi(\pntvec{pq}) \quad \forall \, \pnt{p}, \pnt{q}
    \in A
    \]
    $\varphi$ si dice \emph{isomorfismo associato a $f$}.
\bigskip

Variant with \texttt{esvect}: \quad $ \vv{f(\pnt{p})f(\pnt{q})} \, = \,
    \varphi(\vv{\pnt{pq}}) \quad \forall \, \pnt{p}, \pnt{q}\in A$

\end{document} 

enter image description here

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