IDEAS: Negated double sufficient condition and double NC... Forum

[youknowryan]

If it is not the case that the zoo contains both bears and yaks, then it contains lions and zebras.

Is this the right diagram?

~B & ~Y -> L & Z

~L or ~Z -> B or Y

I know this looks like the SuperPrep B rule, but in this case I am asking about this rule as it stands.

[Asleep]

Not quite. If there are either bears and no yaks or yaks and no bears, then lions and tigers still must be present. It should be written as this:

~(B and Y) -> L and Z

This is equivalent to :
~B or ~Y -> L and Z
-------------------------------------------
The contrapositive is:
~(L and Z) -> ~~ (B and Y)

This is equivalent to:
~L or ~Z -> B and Y

Hope this helps!

[suspicious android]

We just did a whole long thread about this rule like a week ago, coincidentally.