The ten sefirot of direct light, which are enclothed in the ten sefirot of returning light, emerging from the first fusion through collision, are called one sefira. They are named after the highest sefira in that level, despite the fact that it incorporates ten sefirot lengthwise and ten sefirot in its thickness (Talmud Eser Sefirot, v. 3, Q & A 74).
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