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I do not claim that First Order Logic is decidable, but following argument makes it hard for me understand why it is undecidable:

I tried to read proof of "The Undecidability of First Order Logic" from http://kilby.stanford.edu/~rvg/154/handouts/fol.html, but I could not understand it.

- Every 1.-order-logic-formula is either contradictionary or consistent. Such 1.-order-logic-formula, which consistency would be impossible to determine does not exist.
- Therefore it is possible to somehow determine consistency of any 1.-order-logic-formula .
- This method of determining consistent of any 1.-order-logic-formula could be made to an algorithm.

I tried to read proof of "The Undecidability of First Order Logic" from http://kilby.stanford.edu/~rvg/154/handouts/fol.html, but I could not understand it.

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