step 7 -  red
step 7 - green
step 7 - clean
step 8 - red
step 8 - green
step 8 - clean
step 9 - green and clean
step 10  - red
step 10 - red (modified)
step 10- green
step 10 - clean
step 11 - red
step 11 - green
step 11 - clean
step 12 - red
stack test
step 12 - green
step 12 - green and clean
step 13 - red
step 13 - green