[Graphics:submitted.nbgr272.gif] [Graphics:submitted.nbgr273.gif]

For this, we take all variables arbitrary but fixed and try to prove

[Graphics:submitted.nbgr274.gif] [Graphics:submitted.nbgr275.gif]

An attempt for proving this by simplification fails.

Simplification of the lhs term:

[Graphics:submitted.nbgr276.gif]

Simplification of the rhs term:

[Graphics:submitted.nbgr277.gif]