Hypertext links into index

I’m writing up class notes for distribution to the students, and the hypertext package does a bang-up job of making the index into links. I’ve also set up a footer on every page that links to the first page, where the section headers are links to the beginning of each section.

However, I’d like for the section titles, at the top of each page on the left, to be links to the appropriate section in the table of contents. I have no idea how to have the code create a link to a position that is created by the ToC. Currently, those section titles all link to the beginning of the ToC, which is passable, but I’d prefer to link to that section instead of the beginning of the ToC as a whole. Any advice appreciated.

Here is the entirety of the main file, which uses subfiles for most of the content:

documentclass[11pt, letterpaper]{article}

usepackage{subfiles} % these are for splitting the sections into individual files.
usepackage{refcount}
usepackage{xr}
usepackage{titlesec}
newcommand{sectionbreak}{clearpage}

usepackage[head=14pt]{ geometry}
usepackage{fancyhdr}
pagestyle{fancy}
lhead{Mathematical Methods of Physics}                
usepackage[parfill]{parskip}
setlength{parindent}{15pt}
usepackage{graphicx}
usepackage{amssymb}
usepackage{amsmath}
usepackage{indentfirst}
usepackage[shortlabels]{enumitem}
usepackage{soul}
usepackage{setspace}
usepackage{cite,latexsym}
usepackage{url}
usepackage{caption}
usepackage{nicefrac}

usepackage{hyperref}
hypersetup
{
  colorlinks   = true,    % Colours links instead of ugly boxes
  urlcolor     = purple,  % Colour for external hyperlinks
  linkcolor    = blue,    % Colour of internal links
  citecolor    = red      % Colour of citations
}

usepackage{fancyhdr}

pagestyle{fancy}

lhead{hyperref[ToCL]{leftmark}}
rhead{rightmark}
rfoot{hyperref[firstpage]{Mathematical Methods of Physics}}
cfoot{}
lfoot{thepage}



DeclareGraphicsRule{.tif}{png}{.png}{`convert #1 `dirname #1`/`basename #1 .tif`.png}
renewcommand{abstractname}{}
addtolength{topmargin}{-0.25in}
addtolength{textheight}{1.25in}

graphicspath{ {./graphics/} }

setul{4pt}{.4pt}
newcommand{tabletitle}[1]{caption*{ul{#1}}}
newcommand{<}{:!}
newcommand{bull}{, vcenter{hbox{tiny$bullet$}} ,} % middle sized dot, between cdot and bullet, in math mode
newcommand{inv}{:!{text -}1}
newcommand{dd}{mathrm{d}}
newcommand{dx}{mathrm{d}x}
newcommand{ddx}{dfrac{mathrm{d}}{mathrm{d} x} ,}
newcommand{pd}[1]{dfrac{partial}{partial{#1}}}
newcommand{ppd}[2]{dfrac{partial{#1}}{partial{#2}}}
newcommand{R}{mathbb{R}}
newcommand{C}{mathbb{C}}
newcommand{Z}{mathbb{Z}}
newcommand{Q}{mathbb{Q}}
newcommand{I}{mathbb{I}} % capitol letter i, for identity element or matrix
newcommand{ee}{, mathrm{e}}
newcommand{ves}[1]{skew{-2} vec{#1}}
newcommand{px}{partial_x}
newcommand{py}{partial_y}
newcommand{pz}{partial_z}


title{Mathematical Methods of Physics}
author{Martin F. Melhus}
date{today}

parindent=0pt
begin{document}
label{firstpage}
phantomsection

begin{center}

{huge Mathematical Methods of Physics}

vspace{6pt}

Physics 309, section A

Fall 2019
end{center}

vspace{12pt}

Physics 309 covers the mathematical methods of physics.  The class meets three hours a week, at times to be arranged.  The instructor is Professor Martin Melhus.  Dr. Melhus's office is in Kirkbride Hall, room 246, and his campus phone extension is 4377. Dr. Melhus will post his schedule and office hours outside his office; he is also available outside these hours by appointment.

The textbook is emph{Mathematical Methods for Physics and Engineering}, by Riley, Hobson, and Bence, 3$^{rd}$ edition, Cambridge University Press.  References to the text in these notes will simply be page numbers in square brackets [ ].

The class is divided into several sections, each addressing a different topic.  Those topics are:

begin{enumerate}[1.]
item hyperref[sec01]{Fundamentals}
item hyperref[sec02]{Vector Calculus} (Differentiation) % only chapters written so far
item Calculus of Variations
item Generalized Integration
item Complex Variables
item Matrices, Linear Algebra, Vector Spaces, and Function Spaces
item Ordinary Differential Equations (Overview)
item Partial Differential Equations[6pt]
(if time permits)
item Special Functions
item Tensors
end{enumerate}

vspace{6pt}
There will be one oral midterm approximately three fifths of the way through the semester, and a written take home final exam due during finals week.  The instructor may also add a second oral exam as part of the final exam if it is deemed necessary.

Homework will be assigned approximately bi-weekly, with due dates stated as part of the assignment.  Grading for the class will be as follows (subject to modification by the professor):

begin{table}[h]
begin{center}
begin{tabular}{l l l}
Homework & $quad$ & 40%[3pt]
Participation & & 10%[3pt]
Midterm Exam & & 20%[3pt]
Final Exam & & 30%
end{tabular}
end{center}
end{table}

thispagestyle{empty}
phantomsection

tableofcontents

label{ToCL}

pagenumbering{roman}
clearpage

pagenumbering{arabic}
setcounter{page}{1}

subfile{N-01}

subfile{N-02}

%subfile{N-03}

end{document}

Here is the beginning of section 1:

documentclass[main]{subfiles}

ifcsname preamble@fileendcsname
  externaldocument[main-]{main}
  setcounter{page}{getpagerefnumber{main-n01m}}
fi

begin{document}
label{n01}

section{Fundamentals}
label{sec01}

We begin the course by examining the fundamental mathematical principles that we already know, insuring that we understand them to sufficient depth to build a complete and coherent mathematical structure upon them.  Much of this section should be well understood by the student; the professor feels that, despite this, it is best to formalize that understanding.


subsection{Equality}
The idea of equality is so fundamental to mathematics that we must begin by defining the concept of equality, with the following three statements [1064]:

begin{table}[h]
begin{center}
begin{tabular}{l l l}
Reflexive principle & $quad $ &$a = a$[1mm]
Symmetry principle & & If $a = b$ then $b = a$[1mm]
Transitive principle & & If $a = b$ and $b = c$ then $a = c$
end{tabular}
end{center}
end{table}

These principles allow us to understand what constitutes the mathematical concept we call `equals'.  These ideas are so deeply ingrained in our mathematical thinking that we often do not consider them, but simply use them appropriately.  The ideas that they represent, that a thing is equal to itself, that if a first thing is equal to a second then perforce the second thing is equal to the first, and so forth, are fundamental, but need to be examined critically and formalized.


subsubsection{Inequalities}

In addition to equals, $=$, we have a number of other symbols that express a relation between elements of sets.  The more commonly used ones are listed below, and explained.

(and so on, ....)

documentclass{article}
usepackage[colorlinks]{hyperref}
begin{document}
tableofcontents

section{name}

This should also link to the hyperlink{section.1}{section}.
end{document}