We let sqrt{x} mean "square root of x",
and we take i to stand for sqrt{-1} as usual.

            i^2	 =  sqrt{(i^2)^2}
   (sqrt{-1})^2	 =  sqrt{i^4}
             -1	 =  sqrt{1}
             -1	 =  1
             0	 =  2
             0	 =  1.



Most succinct version:
-1 = sqrt( (-1)^2 )
-1 = sqrt( 1 )
-1 = 1.

% A variant of this is found in {\em The Moscow Puzzles}, though
% that's hardly likely to be the first place given.