As per my reading from Wikipedia, the mukhya Upanishads discuss the philosophy of vedas. The seeds of advaita and vishishtadvaita philosophies are found in these upanishads as per my limited readings. Where in samhitas can we find a correlation of the verses in the Samhita and these propounded philosophies such as advaita and vishistadvaita? Also does the Mukhya upanishads make direct references to Samhitha verses in the exposition of their philosophies?