Describe the fundamental stock-flow concepts, variations and how our tools implement them.

• stkflwstock - the similar process driven by demand
• popbirths - animal population process driven by births
• populate - animal population process driven by fertility levels
• selfstkflw - a stock flow process whose stock depends on its’ own output
• stkactflw - evolve a stock by additions and deletions subject to an activity
• stkflwage - stkflwstock with entrant and exit age distributions and promotion
• stkflwflwy - evolve a stock by year built with flows
• stkflwio - evolve a capacity constrained input output system
• stkflwstkshr - evolve a multityped vintaged stock to demand
• stkflwstky - evolve a stock by year built with conversions