What sources do you have available regarding Usuli thought (from Usul al-Fiqh) and the Fiqh of Umar ibn al-Khattab, may Allah be pleased with him?

Usuli thought is a faculty that enables the Usuli scholar to weigh opinions and evaluate inferences. This requires extensive experience in the Quran and its sciences, textual indices, the reliability of narrators, the criteria for preference (tarjih), language sciences, Arab rhetorical styles, and the historical context of texts. The Usuli thinker is characterized by depth. Imam Al-Ghazali and his book "Al-Mustasfa" are considered the pinnacle of Usuli thought, as the science of Usul revolves around four main poles: the ruling (hukm), its source, the methods of derivation and inference, and the inferring mujtahid.