ploting piecewise function in contourplot3d section

*To*: mathgroup at smc.vnet.net*Subject*: [mg111664] ploting piecewise function in contourplot3d section*From*: kamal <azimikamal at gmail.com>*Date*: Mon, 9 Aug 2010 05:15:07 -0400 (EDT)

hi, i want plot x - .5*(y + z) = (250*10^6) when y < .5*(x + z) .5*(y + x) - z = (250*10^6) when y >= .5*(x + z) how can i do that in contourplot3d