4. If the arithmetic sequence $\left\{a_{n}\right\}$ satisfies $a_{2022}=a_{20}+a_{22}=1$, then the value of $a_{1}$ is

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Let $\left\{a_{n}\right\}$ have a common difference of $d$, then $\left\{\begin{array}{l}a_{1}+2021 d=1, \\ a_{1}+20 d=\frac{1}{2}\end{array} \Rightarrow a_{1}=\frac{1981}{4002}\right.$.

