| Bertrand Russell's paradox is sometimes described like this.
|
| In a certain village, the barber shaves all (and only) the men who do not shave themselves.
| Who shaves the barber?
|
| If it's the barber there's a contradiction -- he is shaving himself, but he's only supposed
| to shave those who do not shave themselves.
|
| If someone else shaves the barber, there is also a contradiction -- the barber is
| supposed to shave those who do not shave themselves.
|
| The paradox led to a notion of layering, or stratification, in set theory, designed
| to exclude the problem.
|
| The paradox can be written as a rule for the IBL system as shown below.  However,
| the IBL also has a notion of stratification, and it checks and finds that the
| rule is not meaningful.  It produces a ''Check'' page explaining why.




some-person lives in the village
not : that-person shaves himself
--------------------------------
B shaves that-person


this-person shaves this-other-person
====================================


this-person lives in the village
================================
 A
 B
 C


this-person is a barber
=======================
 B


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| to www.reengineeringllc.com and selecting RussellParadox.