According to the late philosopher and logician George Boolos, who was a professor at MIT, the hardest logical puzzle is one that was invented by the logician and puzzle-master Raymond Smullyan, and modified slightly by the computer scientist John McCarthy. Here is the puzzle :
:cool:
A more elegant way to use SD
Derivation system SD is more elegant than other systems of natural deduction such as that of Copi's, thanks to F.B.Fitch. :smile: Now there is a trend of using SD system in logic books as the only system of natural deduction.
To make the system more elegant...