just checking...

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jfb
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just checking...

Postby jfb » Fri Aug 13, 2010 8:44 pm

F must be played immediately after R, unless G is played earlier than R

this rule would be diagrammed: -RF ---> G...R (if not RF then G before R)

Is that correct??

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Philo38
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Re: just checking...

Postby Philo38 » Fri Aug 13, 2010 8:51 pm

jfb wrote:F must be played immediately after R, unless G is played earlier than R

this rule would be diagrammed: -RF ---> G...R (if not RF then G before R)

Is that correct??


The other way around I think.

Not G . . . R ----> RF

and the contrapositive

Not RF ---> G . . . R

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jfb
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Re: just checking...

Postby jfb » Fri Aug 13, 2010 9:03 pm

Thanks for the response. Anyone else??

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dub
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Re: just checking...

Postby dub » Fri Aug 13, 2010 9:06 pm

I think you've got it right.

CyLaw
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Re: just checking...

Postby CyLaw » Fri Aug 13, 2010 9:07 pm

Philo38 wrote:
jfb wrote:F must be played immediately after R, unless G is played earlier than R

this rule would be diagrammed: -RF ---> G...R (if not RF then G before R)

Is that correct??


The other way around I think.

Not G . . . R ----> RF

and the contrapositive

Not RF ---> G . . . R


Your contrapositive is exactly what OP has. And contrapositives are equivalent statements to the original in logic.

Edit: And yes OP, I think you have it right. If not RF, then G...R must be true.

Edit: Sorry, and all I meant by my first statement is that you always gain the contrapositive for free, so if OP starts with either !G..R -> RF or !RF -> G...R they will gain the other for free.

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jfb
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Re: just checking...

Postby jfb » Fri Aug 13, 2010 9:34 pm

Yes, philo's contrapositive is my original statement, didn't even realize that.

Makes me wonder why would anyone pay for a class when they can just post all of their questions on tls and have them answered within minutes.

Thanks again for the input.

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Philo38
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Re: just checking...

Postby Philo38 » Fri Aug 13, 2010 10:55 pm

:oops:

Sorry, I wasn't paying close attention. Silly mistake, I read wrong.

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Anaconda
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Re: just checking...

Postby Anaconda » Fri Aug 13, 2010 11:04 pm

Correct, whenever you see unless simply make the condition modified by unless your necessary condition and negate the rest and make it your sufficient condition. That's exactly what you did!

PS: you also do this for except, without and until. Don't think I've ever seen those before on LG but I'm sure they've appeared on some hard LR questions.

Examples:

Without crack cocaine you will not become a drug addict.

Drug Addict -> Crack cocaine OR No Crack Cocaine -> Not a Drug Addict

(notice how Drug addict becomes positive because of double negation)
---
Joe won't be a loser unless he has no ambition

Loser -> No Ambition or Ambition -> Not a loser
---
The Cubs won't win the World Series until Hell freezes over

Cubs win WS-> Hell freezes over OR Hell doesn't freeze over -> Cubs don't win WS
---

Pretty easy stuff, just remember the basic rule and that it includes unless, without, except and until.

Not knowing what to do with unless, except, without and until can DESTROY someone on logic games, I think that's how LSAC gets roughs up a lot of kids on a few of the easier games as well as some of the much harder in-out games! If I remember correct the Bird in a Forest game had one conditional rule that included "unless." I bet a lot of kids messed up because they wrote that rule down incorrectly!

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Balthy
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Re: just checking...

Postby Balthy » Sat Aug 14, 2010 12:58 am

Just quickly change "unless" to "if not" and go from there. Makes it much easier.

Correct symbolization is -(G>F) --> RF, so you correctly symbolized the contrapositive.




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