any seeking to comprehend buddhism may find the "upanishads" of invaluable help. i personally recommend deussen's translation, although you may prefer muehler's. a precursor of buddhism.

the only way the "upanishads" are a precursor of Buddhism, is that a small percentage were written first... there is very little evidence that any but a very few were even known during the lifetime of Siddhartha.

upanishads-"commentaries on the vedas". 1200-500BC:vedic era. 1200-900BC:rig veda 900-500BC:later vedas and early upanishads 563-483BC Buddhist chronology.

I'm no expert here, but I have read different.. here!

I think I will have to enlarge my knowledge of the subjecy as I'm sure I would enjoy it.