diff --git a/README.md b/README.md index bf19ad9..2c88c77 100644 --- a/README.md +++ b/README.md @@ -8,9 +8,9 @@ This book will be an undergraduate textbook written in the univalent style, taki - An element of a proposition can be called a *proof*. - Identity types are denoted in general using the macro \eqto, which produces ⥱ (that is an arrow with an = on top). An element of an identity type is called an *identification*, and otherwise a *path*. We may say that it shows how to *identify* two elements. If the type is a set, we may denote its identity types by a = b and call them *equations*. When a = b has an element we say that a and b are *equal*. -- Types similar to identity types, like the type of eqivalences from A to B, are also denoted with a macro ending in "to", like \equivto, producing ⥲ (that is an arrow with an equivalence sign on top). +- Types similar to identity types, like the type of equivalences from A to B, are also denoted with a macro ending in "to", like \equivto, producing ⥲ (that is an arrow with an equivalence sign on top). - The type containing the variable in a family is called the "parameter type", not the "index type", nor the "base type". -- Being equal by definiton is denoted with three lines and is called just that, and not *definitionally equal* or *judgmentally equal*. +- Being equal by definition is denoted with three lines and is called just that, and not *definitionally equal* or *judgmentally equal*. - A synonym of "function" is "map". We don't use "mapping" or "application" as synonyms. - In the preliminary chapters (up to subgroups), the underlying set map U from groups to sets has to be applied explicitly. Thereafter, it can be a coercion. - Composition of p: a⥱b and q: b⥱c is denoted by either p∗q (p\ct q), or by q·p (q\cdot p), qp or q∘p (q\circ p). The latter is preferred when p and q come from equivalences. @@ -36,7 +36,7 @@ This book will be an undergraduate textbook written in the univalent style, taki 10 Κ κ, 11 Λ λ, 12 Μ μ, 13 Ν ν, 14 Ξ ξ, 15 Ο ο, 16 Π π, 17 Ρ ρ, 18 Σ σ, 19 Τ τ, 20 Υ υ, 21 Φ φ, 22 Χ χ, 23 Ψ ψ, and 24 Ω ω; ``` - + for identifiers in the Roman alphabet use the name (e.g., for $\Ker$ use (Ker) or (ker); + + for identifiers in the Roman alphabet use the name (e.g., for $\Ker$ use (Ker) or (ker)); - Given a: A, we refer to elements of a ⥱ a as either symmetries *of* a, or symmetries *in* A. ## Current draft of the book diff --git a/circle.tex b/circle.tex index a97bc7c..04bd9d5 100644 --- a/circle.tex +++ b/circle.tex @@ -627,7 +627,7 @@ \section{\Coverings} the other interpretation ``all the preimages are connected'' would simply give us an equivalence (since connected sets are contractible), and this is \emph{not} what is intended. (Equivalences are \coverings, -but not necessarily connected \coverings and connected \coverings are not neccesarily equivalences.) +but not necessarily connected \coverings and connected \coverings are not necessarily equivalences.) Likewise for the other qualifications; for instance, in a ``finite \covering'' $f:A\to B$, all fibers are finite sets, but @@ -3344,7 +3344,7 @@ \section{Universal property of $\Cyc_n$} $\hat p_x(\blank\sigma_n) = \hat p_x(\blank) \sigma$. By setting $p \jdeq \hat p_{\pt_n}(\refl {\pt_n})$, we would have succeeded. Indeed, path induction on $\alpha: x \eqto x'$ shows that $\hat p_{x'}(\alpha \blank) = \ap f (\alpha) \hat - p_x(\blank)$ on one hand, and the hyptohesis on $\hat p$ proves that $\hat + p_x(\blank)$ on one hand, and the hypothesis on $\hat p$ proves that $\hat p_{\pt_n} (\blank) \sigma = \hat p_{\pt_n}(\blank \sigma_n)$ on the other hand. This leads to the chain of equations: \begin{align*} diff --git a/fingp.tex b/fingp.tex index 5497544..5ce9aa5 100644 --- a/fingp.tex +++ b/fingp.tex @@ -44,7 +44,7 @@ \section{Brief overview of the chapter} \label{sec:fingp-overview} We start by giving the above-mentioned counting version \cref{lem:Lagrangeascounting} of Lagrange's theorem \cref{thm:lagrange}. We then moves on to prove Cauchy's \cref{thm:cauchys} stating that any finite group whose cardinality is divisible by a prime $p$ has a cyclic subgroup of cardinality $p$. -Cauchchy's theorem has many applications, and we use it already in \cref{sec:sylow} in the proof of Sylow's Theorems which give detailed information about the subgroups of a given finite group $G$. Sylow's theorems is basically a study of the $G$-set of subgroups of $G$ from a counting perspective. +Cauchy's theorem has many applications, and we use it already in \cref{sec:sylow} in the proof of Sylow's Theorems which give detailed information about the subgroups of a given finite group $G$. Sylow's theorems is basically a study of the $G$-set of subgroups of $G$ from a counting perspective. In particular, if $p^n$ divides the cardinality of $G$, but $p^{n+1}$ does not, then Sylow's Third \cref{thm:sylow3} gives valuable information about the cardinality of the $G$-set of subgroups of $G$ of cardinality $p^n$. @@ -137,7 +137,7 @@ \section{Cauchy's theorem} % $$A(S,j)\defequi ((S,j)=(S,j)\to \USym G).$$ Since we have an equivalence $j^?:\bn p\to ((S,j)=(S,j))$ we get that $J:A(S,j)\to \prod_{\bn p}\USym G$ given by $J(g)=(g_{j^0},g_{j_1},\dots,g_{j^{p-1}})$ is an equivalence. Given a set $A$, a function $a : \bn p \to A$ is an ordered $p$-tuple of elements of $A$: it suffices to write $a_i$ for $a(i)$ to retrieve the usual notations for tuples. Given $(S,j) : \B\CG_p$ however, functions $S \to A$ cannot really be thought the same because $S$ is not -explicitely enumerated. But as soon as we are given $q : \zet/p \eqto (S,j)$, then functions $S \to A$ are just as good to model ordered +explicitly enumerated. But as soon as we are given $q : \zet/p \eqto (S,j)$, then functions $S \to A$ are just as good to model ordered $p$-tuples of $A$ (just by precomposing with the first projection of $q$). With this in mind, define $\mu_p : (\bn p \to \USym G) \to \USym G$ to be the $p$-ary multiplication, meaning $\mu_p (g) \defequi g_0g_1\ldots g_{p-1}$. Then, one can define $\mu:\prod_{(S,j):\B\CG_p}(\zet/p \eqto (S,j)) \to (S\to\USym G)\to \USym G$ by $\mu_{(S,j)}(q)(g)\defequi (gq)_{0}\cdot\dots\cdot (gq)_{p-1}$ diff --git a/galois.tex b/galois.tex index e46fe6c..c98654d 100644 --- a/galois.tex +++ b/galois.tex @@ -4,7 +4,7 @@ \chapter{Galois theory}% %% VERY PRELIMINARY The goal of Galois theory is to study how the roots of a given polynomial can be distinguished from one another. Take for example $X^2+1$ as a polynomial -with real coefficients. It has two distincts roots in $\mathbb C$, namely $i$ +with real coefficients. It has two distinct roots in $\mathbb C$, namely $i$ and $-i$. However, an observer, who is limited to the realm of $\mathbb R$, can not distinguish between the two. Morally speaking, from the point of view of this observer, the two roots $i$ and $-i$ are pretty much the same. Formally @@ -12,7 +12,7 @@ \chapter{Galois theory}% satisfied if and only if $Q(-i,i) = 0$ also. This property is easily understood by noticing that there is a automorphism of fields $\sigma: \mathbb C \to \mathbb C$ such that $\sigma(i) = -i$ and $\sigma(-i) = i$ which also fixes -$\mathbb R$. The goal of this chapter is to provide the rigourous framework in +$\mathbb R$. The goal of this chapter is to provide the rigorous framework in which this statement holds. {\color{red} TODO: complete/rewrite the introduction} @@ -143,7 +143,7 @@ \section{Covering spaces and field extensions} equivalence. However, the converse is false, as shown by the non-algebraic extension $\mathbb Q \hookrightarrow \mathbb R$. We will prove that every $\mathbb Q$-endomorphism of $\mathbb R$ is the identity function. Indeed, any - $\mathbb Q$-endormorphism $\varphi : \mathbb R \to \mathbb R$ is linear and + $\mathbb Q$-endomorphism $\varphi : \mathbb R \to \mathbb R$ is linear and sends squares to squares, hence is non-decreasing. Let us now take an irrational number $\alpha:\mathbb R$. For any rational $p,q:\mathbb Q$ such that $p < \alpha < q$, then $p = \varphi(p) < \varphi(\alpha) < \varphi(q) = q$. Hence @@ -171,7 +171,7 @@ \section{Intermediate extensions and subgroups} characterize those extensions $i':k \to L$ for which all subgroups of $\Gal(L,i')$ arise in this way. -Given any extension $i:k \to L$, there is an obivous $\Gal(L,i)$-set $X$ given by +Given any extension $i:k \to L$, there is an obvious $\Gal(L,i)$-set $X$ given by \begin{displaymath} (L',i') \mapsto L'. \end{displaymath} @@ -181,7 +181,7 @@ \section{Intermediate extensions and subgroups} K \defequi (Xg)^{\mkgroup B} \jdeq \prod_{x:B}X(g(x)) \end{displaymath} It is a set, which can be equipped with a field structure, defined pointwise. -Morevover, if one denotes $b$ for the distinguished point of $B$, and $(L'',j'')$ for $g(b)$, then, because $g$ is pointed, one has a path $p:L=L''$ such that $pi'=j''$. There are +Moreover, if one denotes $b$ for the distinguished point of $B$, and $(L'',j'')$ for $g(b)$, then, because $g$ is pointed, one has a path $p:L=L''$ such that $pi'=j''$. There are fields extensions $i':k \to K$ and $j':K \to L$ given by: \begin{displaymath} i'(a) \defequi x\mapsto \snd(g(x))(a),\quad @@ -189,7 +189,7 @@ \section{Intermediate extensions and subgroups} \end{displaymath} In particular, for all $a:k$, $j'i'(a) = \inv p \snd(g(b))(a) = \inv p j''(a) = i'(a)$. -Galois theory is interested in the settings when these two contructions are inverse from each other. +Galois theory is interested in the settings when these two constructions are inverse from each other. \section{separable/normal/etc.} \label{sec:cover-spac-fields-1} diff --git a/geometry.tex b/geometry.tex index 89804e0..88f153e 100644 --- a/geometry.tex +++ b/geometry.tex @@ -272,7 +272,7 @@ \section{Geometric objects} \begin{definition} Given an type $I$ and a family of geometric objects $T_i$ parametrized by the elements of $I$, an {\em arrangement} of the objects is a - configuration, also parametrized by the elements of $I$, whose $i$-th consituent is merely equal to + configuration, also parametrized by the elements of $I$, whose $i$-th constituent is merely equal to $T_i$. \end{definition} diff --git a/group.tex b/group.tex index 99966df..433a5c9 100644 --- a/group.tex +++ b/group.tex @@ -2826,7 +2826,7 @@ \subsection{Center of a group} There is a natural map $\ev_{\shape_G} : (\BG_\div\eqto\BG_\div) \to \BG_\div$ defined by $\ev_{\shape_G}(\varphi)\defequi \varphi(\shape_G)$, where the path -$\varphi$ is coerced to a funciton through univalence. In particular, +$\varphi$ is coerced to a function through univalence. In particular, $\ev_{\shape_G}(\refl{\BG_\div}) \jdeq \shape_G$. It makes the restriction of this map to the connected component of $\refl{\BG_\div}$ a pointed map. In other words, it defines a group @@ -3067,7 +3067,7 @@ \subsection{Universal cover and simple connectedness} $\trp[\setTrunc{a\eqto\blank}]p$ is equal to the function $\alpha\mapsto \settrunc{p}\cdot \alpha$. In particular, there exists an equivalence from the type of path between two points $(x,\alpha)$ and -$(y,\beta)$ of the universal cover $\univcover A a$ to sum type, analagous to +$(y,\beta)$ of the universal cover $\univcover A a$ to sum type, analogous to the identification of paths in sum types: \begin{equation} \label{eq:id-types-universal-cover}% @@ -3117,7 +3117,7 @@ \subsection{Universal cover and simple connectedness} determined by $\varphi_x \circ \settrunc\blank : a \eqto x \to \inv f (x)$. By induction on $p : a \eqto x$, we prove that $\varphi_x (\settrunc p) = \trp [\inv f] p (b , f_0) $ where $b$ is the element pointing $B$ and $f_0$ the path pointing $f$. Indeed, for $p \jdeq \refl a$, we get $\varphi_a (\settrunc {\refl a}) \jdeq (\varphi (\settrunc {\refl a}) , q_{\settrunc {\refl a}}) = (b , f_0)$ - because $q$ is an indentification $\fst \eqto f \varphi$ of pointed functions. + because $q$ is an identification $\fst \eqto f \varphi$ of pointed functions. \end{proof} \subsection{Abelian groups and simply connected $2$-types}