### 1.2.3.4 Russell's Paradox

Unfortunately, it became evident that the Principia ( although a monumental work ) was flawed.

Some logical paradoxes had been found which caused great problems. One of these is as follows

- sets, that contain themselves

sets that do not contain themselves

Any set either belogns to or to

Let A be to set of all sets that do not contain themselves

Does A

Does A

Must redefine the meaning of