Simulation Tree:
  SM_PPL
    AR(Inventory Accounting Transaction)
      SM_IAT(ledger=A)
      SM_IAT(ledger=B)

Where SM_IAT.isBuildable() returns True iff:
  * SM_IAT(ledger=A): SM_PPL delivery state == 'started' (Shipped).
  * SM_IAT(ledger=B): SM_PPL delivery state == 'stopped' (Received).

Defining this in a single BP lead to the following Business Links:
  * BL_PPL_started:
    - predecessor=trade/ordered
    - successor=trade/delivery_started
    - completed_state_list=['started']
    - trade_phase=trade/delivery
  * BL_IAT_ledger_A:
    - predecessor=trade/delivery_started
    - successor=trade/inventory_accounted
    - trade_phase=trade/inventory_accounting
    - predicate: ledger == A

  * BL_PPL_delivered:
    - predecessor=trade/ordered
    - successor=trade/delivered
    - completed_state_list=['stopped', 'delivered']
    - trade_phase=trade/delivery
  * BL_IAT_ledger_B:
    - predecessor=trade/delivered
    - successor=trade/inventory_accounted
    - trade_phase=trade/inventory_accounting
    - predicate: ledger == B

This means that SM_PPL will have both BL_PPL_started and
BBL_PPL_delivered Business Links as causality which was not handled
by isBuildable.

Another solution would have been to add this logic on the Builder
'Simulation Select Method' but IMO this should not be done there.