= Solution
A <tensor product of group representations> has <character> equal to the product of its factor <characters>. Multiplying the rows of the <character table> in <1/b/solution>, using $s^2=2+t$, $t^2=2+s$ and $st=-1$, gives all the <Clebsch-Gordan decomposition of group representations>:
$$
\boxed{\begin{array}{c|cccc}
\otimes&R_0&R_1&R_2&R_3\\\hline
R_0&R_0&R_1&R_2&R_3\\
R_1&R_1&R_0&R_2&R_3\\
R_2&R_2&R_2&R_0\oplus R_1\oplus R_3&R_2\oplus R_3\\
R_3&R_3&R_3&R_2\oplus R_3&R_0\oplus R_1\oplus R_2
\end{array}}
$$
For example, the <character> of $R_2\otimes R_2$ is $(4,s^2,t^2,0)=(4,2+t,2+s,0)$, the sum of the <characters> of $R_0$, $R_1$ and $R_3$. Likewise $R_2\otimes R_3$ has <character> $(4,-1,-1,0)=\chi_2+\chi_3$. The <trivial representation> and $R_1\otimes R_1=R_0$ account for the remaining entries.
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