2. Goods i and j are said to be "substitutes" (at (p, u)) if op, Ohi (p, u) 2 0. (a) If goods i and j are substitutes at (p, u) is it always the case that goods j and i are substitutes at (p, u)? (b) Give an example of two goods for which it is plausible to think that they would be substitutes for a consumer at one price and not substitutes at another price