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We prove **forall** x in **R**: `x`*`x` != -1. Take arbitrary
`x` in **R**.

*If*, then`x`>= 0`x`*`x`>= 0.*If*, then also`x`< 0`x`*`x`>= 0.

Author: Wolfgang Schreiner

Last Modification: November 30, 1999