∑ Oxk(p, w D Ox(p, w) 0 L ∑ oxk(p,w) pi Oxk(p, w) api Xk =∑ ￡D,+￡ This tells you that for any commodity, the sum of own and cross price elasticities equals-1 times the income elasticity i1 L xkp,w pi pi  xkp,w w w  0  i1 L xkp,w pi pi xk  xkp,w w w xk   i1 L pi k  w k  0 This tells you that for any commodity, the sum of own and cross price elasticities equals -1 times the income elasticity