A test of Equation Numbering

---

Equation: $$\begin{equation} E = mc^2 \end{equation}$$ Equation*: $$\begin{equation*} E = mc^2 \end{equation*}$$

---

Brackets: $$E = mc^2$$ Brackets tagged: $$E = mc^2\tag{x}$$

---

Split: $$\begin{equation} \begin{split} a& =b+c-d\\ & \quad +e-f\\ & =g+h\\ & =i \end{split} \end{equation}$$

---

Multline: $$\begin{multline} a+b+c+d+e+f+g\\ M+N+O+P+Q\\ R+S+T\\ u+v+w+x+y+z \end{multline}$$ Multline*: $$\begin{multline*} a+b+c+d+e+f+g\\ M+N+O+P+Q\\ R+S+T\\ u+v+w+x+y+z \end{multline*}$$

---

Gather: $$\begin{gather} a_1=b_1+c_1\\ a_2=b_2+c_2-d_2+e_2 \end{gather}$$ Gather*: $$\begin{gather*} a_1=b_1+c_1\\ a_2=b_2+c_2-d_2+e_2 \end{gather*}$$

---

Align: $$\begin{align} a_1& =b_1+c_1\\ a_2& =b_2+c_2-d_2+e_2 \end{align}$$ Align*: $$\begin{align*} a_1& =b_1+c_1\\ a_2& =b_2+c_2-d_2+e_2 \end{align*}$$ Align: $$\begin{align} a_{11}& =b_{11}& a_{12}& =b_{12}\\ a_{21}& =b_{21}& a_{22}& =b_{22}+c_{22} \end{align}$$ Align with \notag and \tag: $$\begin{align} a_{11}& =b_{11}& a_{12}& =b_{12}\notag\\ a_{21}& =b_{21}& a_{22}& =b_{22}+c_{22} \tag{y} \end{align}$$ Align* with \tag: $$\begin{align*} a_1& =b_1+c_1\tag{z}\\ a_2& =b_2+c_2-d_2+e_2 \end{align*}$$