Some people worry that the mathematicians are passing into mysticism when we talk about infinity and negative infinity. However, when we write {{MATH_173}} all we mean is that as {{MATH_174}} approaches {{MATH_175}}, {{MATH_176}} becomes arbitrarily large and {{MATH_177}} becomes arbitrarily large, with {{MATH_178}} taking negative values. We're using {{MATH_179}} to indicate directions, rather than a specific value. {{CMD_180}}