Math Is Fun Forum

mrpace

Member

Registered: 2012-08-16

Posts: 88

Help with logic question please

Show that it is valid to infer that, provided there are some stones, if every god lifts every stone, then there is a stone which every god lifts.

So this is what I get as the schema

Px = x is a God
Qx = x is a stone
Rxy = x lifts y

∀x(Px ⊃ ∀y(Qy ⊃ Rxy)      ⊃      ∃y(Qy ∧ ∀x(Px ⊃ Rxy))
1                                  0       0

My problem is that there is no weak quantifier. Usually I solve these by finding the weak quantifiers and creating a-rows and b-rows....however I have no idea what to do when every quantifier is strong.

Help???

Olinguito

Member

Registered: 2014-08-12

Posts: 649

Re: Help with logic question please

You need to use the fact that there are some stones:

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Bassaricyon neblina