x_j and where is strictly smaller than
In the US, there is no industry-standard, 100% objective scale for mattress firmness. How firm or soft something feels ultimately depends on factors like your body type and sleeping position. Brands will also sometimes use words like “plush” to describe softness, for example, or “luxury firm” to describe a mattress that’s somewhere between soft and firm.，详情可参考PDF资料
«Решетнев» рассказал о сборке спутника «Ямал-501»14:53。关于这个话题，PDF资料提供了深入分析
Dictionary comprehension based syntax for creating typed dicts and protocols