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- October 22nd 2008, 12:32 PMprincessleia[SOLVED] Propositional functions and quantifiers ...
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- October 22nd 2008, 01:09 PMPlato
- October 22nd 2008, 06:03 PMpoutsos.B

To express in quantifier notation that Al and Sue**have**exactly one child we write:

[ F( A,y) & M( S,y)] ,which means there is a unique child (y) ,lets say ,of whom Al and Sue are the father and mother respectively:

Now that formula is equivalent to the following formula:

[ F( A,y) & M( S,y)]& {[F( A,y) & M( S,Y)] & [ F( A,z) & M( S,z)]------> y=z}:

The 2nd formula means that Sue and Al have a child and their child is the only one (expressed by the 2nd part of the formula: {[F( A,y) & M( S,Y)] & [ F( A,z) & M( S,z)]------> y=z}:

NOW if my 2nd formula is equivalent to that given by Plato ,one should be able to prove that.

I think it is a good exercise for**you**