first failed test
subtract failed
corrected
multiply error
multiply fixed
divide fail
divide fixed
power fail
powers fixed
test_add_1 fail
test_add_1 fixed
test_add_2 fail
test_add_2 fixed
test_subtract_1 fail
test_subtract_1 and test_add_1 fixed
test_subtract_2 failed
test_subtract_2 fixed
step 10-1 fail
step 10-1 fixed
step 10-2 fail