$\left(1\right)\frac{\lambda}{\pi {\in}_{0}a}\phantom{\rule{0ex}{0ex}}\phantom{\rule{0ex}{0ex}}\left(2\right)\frac{\lambda}{2\pi {\in}_{0}a}\phantom{\rule{0ex}{0ex}}\phantom{\rule{0ex}{0ex}}\left(3\right)\frac{\lambda}{4\pi {\in}_{0}a}\phantom{\rule{0ex}{0ex}}\phantom{\rule{0ex}{0ex}}\left(4\right)\frac{2\lambda}{\pi {\in}_{0}a}$

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