The Short-run Aggregate Supply Curve (SPAS is upward sloping because1)
1) a ceteris paribus increase in the price index causes firms' real costs of production to decrease in the short run because nominal wages adjust more slowly than the rate of inflation in the short run
2) a cetens paribus increase in the amount of natural resources the economy has will increase potential real GDP
3) a ceteris paribus increase in nominal wages causes firms real costs of production to increase because nominal wages adjust to a ceteris paribus change faster than the rate of inflation in the Short run.
4) in the short run, cetens panbus changes in the pros index have no effect on real GDP.