Below is a table that illustrates four different supply chain processes for the publishing industry.

$\backslash$table$[[\backslash$table$[[$Supply chain$],[$Cycles$]],$Barnes and Noble,Amazon$/$Penguin$,$Digital,$\backslash$table$[[$Digital Self$],[$publishing$]]],[$Innovation$,$Author,Author,Author,Author$],[$Innov$\text{'}$n$/$Supplier$,$Editor,Editor,Editor,$],[$Supplier$,$Publisher,Publisher,Publisher,$],[$Manufacturer$,$Book manufacturer,Book manufacturer,,$],[$Distributor$,$Distributor,Distributor,,$],[$Retailer$,$Retail,,,$],[$Customer$,$Customer,Customer,Customer,Customer$]]$

Answer each questions below in $1-2$ sentences.

a$)$ What is a process cycle?

b$)$ Define the push$/$pull boundary.

c$)$ For each book supply chain process, where is the push$/$pull boundary

d$)$ Some of the supply chain processes above do not have a specific cycle. Does the process cycle disappear, or does it merge into another cycle? Give an example from the article.