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![`and`(`/`(`*`(x[a]), `*`(x[d])) = `/`(`*`(y[a]), `*`(y[d])), `and`(`/`(`*`(y[a]), `*`(y[d])) = -2, `and`(-2 = `+`(`*`(4, `*`(`/`(-2)))), `+`(`*`(4, `*`(`/`(-2)))) = -2)))](images/m_21.gif){kind=small}