Is this a bug

*To*: mathgroup at smc.vnet.net*Subject*: [mg84243] Is this a bug*From*: "huxiaopengstat at gmail.com" <huxiaopengstat at gmail.com>*Date*: Sat, 15 Dec 2007 15:36:54 -0500 (EST)

Clear[f] f[x_] := x^2 + 1 /; x >= O f[x_] := -x^2 - 1 /; x < O Plot[f[x], {x, -2, 2}] Above f is a piecewise function.But Plot can't plot the function. Why? MY MATHEMATICA is version 6. can the piecewise function be defined like this?