* Principia Mathematica* is the book Russell wrote with Alfred North
Whitehead where they gave a logical foundation of Mathematics by developing the Theory of Types that obviated the Russell's paradox. This

assertion may become more convincing after a look at the page 362 of
*Principia Mathematica* where Russell and Whitehead finally proved that 1 + 1 = 2.

You are visitor number [an error occurred while processing this directive] since 2001-11-15