__x__+ __y__+ ___z_ = 1
x+y+z x+y+z x+y+z
_____________________________
_x+ y_ + _x+ z:_ + _y+ x_ =?
x+y+z x+y+z x+y+z
__x__+ __y__+ ___z_ = 1 ⇒ _ x+ y+ z_ = 1
x+y+z x+y+z x+y+z x+y+z
_x+ y_ + _x+ z:_ + _y+ x_ =?
x+y+z x+y+z x+y+z
_x+ y_+_x+ z:_+_y+ x_ =
x+y+z
_2x+2y+2z_ =
x+y+z
_2(x+y+z)_ =
x+y+z
2