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I read that mathematical logic can have a "semi-definite" question but what does it mean and is there an easy example? Is it a yes-or-no question where there is no method for one of the answers?

For example, you state P(x,y) and only given that it is true, there is a method to prove it and there is no method to prove it if it is false.

Did I understand?

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  • $\begingroup$ Where did you read this? "semi-definite" is not a standard term. Yes, it's true that there's a mechanical way (an algorithm) to show that a statement follows from other statements when it does follow, and that in general there isn't an algorithm to show that a statement does not follow from others. ¶ Whether you understood or not depends on what the text you read says :) $\endgroup$ – BrianO May 19 '16 at 11:05
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    $\begingroup$ Maybe Semidecidable ? $\endgroup$ – Mauro ALLEGRANZA May 19 '16 at 11:18
  • $\begingroup$ I have the lecture notes and can look at it again. It was the lecture notes where the course book was Symbolic Logic by Graeme Forbes. $\endgroup$ – Niklas Rosencrantz May 19 '16 at 12:58

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