Conditional pageref for labels far away

Question

Currently, within my thesis, I am numberings theorems (and remarks, etc.) with a global counter. This makes it difficult in the printed version to find the theorem if a reference is too far away from the label. Is there any simple way I can modify my reference commands to add a "on page XXX" in case of having lets say a 3 page gap between ref and label? Do you have any suggestions or experiences?

As far as I understood the documentations, packages such as varioref only support a one-page-diff condition; but even this I was not able to activate.

Minimal working example:

\documentclass{scrreprt}

\usepackage{blindtext} % lore ipsum...
\usepackage{amsthm}
\newtheorem{thm}{Theorem}

\begin{document}
  % example theorem:
  \begin{thm}\label{thm:foo}
    The future belongs to those who believe in their dreams.
  \end{thm}
  % generate more than 3 pages of text:
  \blindtext[20] 
  % reference:
  Reference to theorem \ref{thm:foo}. Here an automatic
  ``on page \pageref{thm:foo}'' would be nice.
\end{document}

MWE for Mico (see discussion below):

\documentclass{scrreprt}
\usepackage{blindtext} % lore ipsum...
\usepackage{amsmath}
\usepackage{ntheorem}
\usepackage{varioref}
\usepackage{hyperref}
\newtheorem{thm}{Theorem}

\begin{document}
  % theorem foo
  \begin{thm}\label{thm:foo}
      The future belongs to those who believe in their dreams, see (\vref{eqn:bar})
  \end{thm}

  % some pages of text...
  \blindtext[15]

  % cross-reference to theorem within equation which is labeled itself (same works for figures)
  \begin{align}\label{eqn:bar}
    a+b=c\quad\text{(cf. Theorem \vref{thm:foo})}
  \end{align}
\end{document}

Leads to

• ! Package amsmath Error: Multiple \label's: label 'eqn:bar' will be lost.
• ! Package amsmath Error: Multiple \label's: label '4@xvr' will be lost.
• several further warnings...

(Partial) Solution (based on Christians idea) After playing around with Christians suggestion I came up with a solution (it SEEMS to work). I have to store the manipulated \ref command to \vref before hyperref is loaded. Then, I can use \ref as standard ref and \vref as optional "on page" version. For some strange reason this only works together with babel. It is important to add a "%" in order to avoid wrong spacing.

\documentclass{scrreprt}
\usepackage{blindtext} % lore ipsum...
\usepackage{amsmath}    
\usepackage[english]{babel} % < for some strange reason HAS to be loaded
%% --- ref manipulations as suggested by Christian Hupfer:
\makeatletter
\let\latex@@ref\ref

\newcounter{pagegaptreshhold}
\setcounter{pagegaptreshhold}{2}

\newcounter{tmpcntr}

\renewcommand{\ref}[1]{%
  \setcounter{tmpcntr}{\value{page}}%
  \addtocounter{tmpcntr}{-\getpagerefnumber{#1}}%
  \ifnum\value{tmpcntr} < 0 %
  \setcounter{tmpcntr}{\numexpr -1*\value{tmpcntr}}%
  \fi%
  \ifnum\value{tmpcntr} > \value{pagegaptreshhold}
  \latex@@ref{#1} on page \pageref{#1}%
  \else%
  \latex@@ref{#1}%
  \fi%
}
\makeatother
%% --- end cmhughes suggestion ---
\let\vref\ref
\usepackage{hyperref}

\newtheorem{thm}{Theorem}
\begin{document}
  % theorem foo
  \begin{thm}\label{thm:foo}
      The future belongs to those who believe in their dreams, see (\vref{eqn:bar})
  \end{thm}

  % some pages of text...
  \blindtext[30]

  % cross-reference to theorem within equation which is labeled itself (same works for figures)
  \begin{align}\label{eqn:bar}
    a+b=c\quad\text{(cf. Theorem \vref{thm:foo})}
  \end{align}
  In particular, we have now the choice between 
  \begin{itemize}
    \item ``on page''-if-too-far-away-style: Theorem \vref{thm:foo}
    \item classic style: Theorem \ref{thm:foo}
  \end{itemize}
\end{document}

Answer 1

(Updated answer after the OP posted a second, more elaborate MWE.)

The varioref package implements the following decision rule with regard to generating page call-outs:

• If the item being cross-referenced and the cross-reference are on the same page, no page-related affix is produced;

• If the item being cross-referenced and the cross-reference are on adjoining pages, either "on the previous page" or "on the following page" is affixed to the cross-reference.

• If the item being cross-referenced and the cross-reference itself are two or more pages apart, a "on page x" affix is generated.

If you know in advance that there will be several pages between the cross-reference and the item being cross-referenced, you may also use the instruction \fullref, which is simpler (uses fewer machine cycles...) than \vref.

If you use both varioref and hyperref, you should load the cleveref package as well: Doing so fixes a (mild) conflict between the former two packages. If you load cleveref, the items' names ("equation", "theorem", etc) will be prefixed automatically to the cross-reference call-outs.

\documentclass{scrreprt}
\usepackage{blindtext}    % lorem ipsum...
\usepackage{amsmath}
\usepackage[amsmath]{ntheorem}

\usepackage{varioref}     % for \vref and \fullref macros
\usepackage[colorlinks]{hyperref}
\usepackage[nameinlink]{cleveref}

\newtheorem{thm}{Theorem}

\begin{document}
\setcounter{chapter}{1} % just for this example

% theorem foo, with cross-reference to an equation
\begin{thm}\label{thm:foo}
The future belongs to those who believe in their dreams (see \vref{eqn:bar}). 
\end{thm}

% some pages of text...
\blindtext[15]

% equation bar, with cross-reference to a theorem 
\begin{align}\label{eqn:bar}
    a+b=c\quad\text{(cf.\ \fullref{thm:foo})}
\end{align}
\end{document}

Answer 2

\documentclass{article}

\usepackage{refcount}
\usepackage{blindtext}

\makeatletter
\let\latex@@ref\ref

\newcounter{pagegaptreshhold}
\setcounter{pagegaptreshhold}{2}

\newcounter{tmpcntr}

\renewcommand{\ref}[1]{%
  \setcounter{tmpcntr}{\value{page}}%
  \addtocounter{tmpcntr}{-\getpagerefnumber{#1}}%
  \ifnum\value{tmpcntr} < 0 %
  \setcounter{tmpcntr}{\numexpr -1*\value{tmpcntr}}%
  \fi%
  \ifnum\value{tmpcntr} > \value{pagegaptreshhold}
  \latex@@ref{#1} on page \pageref{#1}%
  \else%
  \latex@@ref{#1}%
  \fi%
}
\makeatother

\begin{document}

\section{first} 
In\ref{section::second} we will see that...
\blindtext[40]
\section{second} \label{section::second}
Here: \ref{section::second}

\end{document}