[(5,5),(5,0)] to [(10,5),(0,0)] only Competitive equilibrium at price (0, Py)
if we set P = (Px, 0) then individual 2 will demand 10 unit of y in order to maximize his utility at these price, which is not possible in competitive equilibrium
and at any positive price => No competitive equilibrium
Had individual 2's utility increased as a result of more x, would this not be an equilibrium then?
So if there's any way to reallocate such that demand is not equal to supply in the true sense, but utility from reallocation does not change the utilities from the demanded sets, then that's a competitive equilibrium too?
Solution of the above problem is
x = y if the price of both good are positive
x may or not equal to y if the price of 1 good equal to 0, because demanding extra amount a good whose price equal to 0, does not change the optimal solution of the problem just because it doesn't change budget constraint and the utility.