Which of the following statements is incorrect?

a$.$ The Form $6251$ uses the indirect method to calculate the AMT.

b$.$ In the indirect calculation, only amounts that differ between regular tax and AMT are included in the AMTI calculation.

c$.$ AMTI calculated under the direct and indirect methods will result in the same AMTI amount.

d$.$ AMTI calculated under the direct and the indirect methods produces different AMTI amounts.