How would one create these curved arrows?

Question

I was wondering how would one create such a diagram with curved arrows with LaTeX. I have no idea where to begin with this, so any help would be appreciated.

Answer 1

Welcome! With tikz-cd.

\documentclass{article}
\usepackage{tikz-cd}
\begin{document}
\[
\begin{tikzcd}[every arrow/.append style={-stealth}]
\cdots \arrow[r]& H^k(B) \arrow[r]& H^k(C)\arrow[r] & H^k(D)
 \arrow[dll,out=-10,in=170,overlay,looseness=1.2,"\delta" {marking,fill=white}]\\
 & H^{k+1}(B)\arrow[r] & H^{k+1}(C)\arrow[r] & H^{k+1}(D) 
  \arrow[dll,out=-10,in=170,overlay,looseness=1.2,"\delta" {marking,fill=white}]\\
 & H^{k+2}(B) \arrow[r]& H^{k+2}(C)\arrow[r] &\cdots \\ 
\end{tikzcd}
\]
\end{document}

See this post, this post, this post, and this post for related answers. Big thanks to Torbjørn T. for sharing these with me.

Answer 2

With the matrix library of TikZ:

\documentclass[tikz,border=3.14]{standalone}

\usetikzlibrary{matrix}

\begin{document}
\begin{tikzpicture}
  \matrix (H) [matrix of math nodes, column sep=4ex, row sep=1ex]
    {%
      \vphantom{H}\ldots & H^k(B) & H^k(C) & H^k(D) \\
             & H^{k+1}(B) & H^{k+1}(C) & H^{k+1}(D) \\
             & H^{k+2}(B) & \vphantom{H}\ldots \\
    };
  \draw[->] (H-1-1) -- (H-1-2);
  \foreach\r in {1,2}
    \foreach\n in {2,3}
      \draw[->] (H-\r-\n) -- (H-\r-\the\numexpr\n+1\relax);
  \draw[->] (H-3-2) -- (H-3-3);
  \foreach\r in {1,2}
    \draw[->] (H-\r-4.east) to[out=-10,in=170]node[fill=white,inner
    sep=1pt]{$\delta$} (H-\the\numexpr\r+1\relax-2.west)
    ;
\end{tikzpicture}
\end{document}