[bsip18] updates

bsip-0018.md

@@ -17,6 +17,9 @@ continued and put to good use again.
 
 # Motivation
 
+The necessity of reviving bitassets has already been discussed in
+BSIP-0017, and is unquestioned.
+
 Market-pegged assets, aka SmartCoins are among the core features of the
 BitShares blockchain and as such provide one of our unique selling points.
 
@@ -72,7 +75,43 @@ global settlement or margin call right away.
 
 # Specifications
 
-## `obtain_settlement_funds_operation`
+## Bugfix: MPAs that have seen a global settlement cannot be settled after the price feed expires
+
+It has turned out that force-settling an MPA requires a valid price feed
+even when the MPA has a `settlement_price` set. This is clearly a bug,
+since in that case the settlement price is independent from the price
+feed. Furthermore, publishing price feeds is no longer possible after a
+global settlement, so the time when settlement is possible at all is
+limited to the expiration period of the price feed of the MPA.
+
+This bug will be fixed. See
+https://github.com/cryptonomex/graphene/issues/664#issuecomment-254056746
+for a discussion.
+
+## Auto-revive empty bitassets
+
+A bitasset is "empty" if nobody is holding a positive amount of it
+anymore. The only reasonable exception to this rule is the pool of
+accumulated fees belonging to the asset itself. This situation can occur
+after all holders of a globally settled asset have settled their
+position via forced settlement.
+
+The emptiness of a bitasset can easily be determined. When the BitAsset is
+empty, the remainder of the settlement fund will be paid out to the
+issuer, the accumulated fees and the current supply are reset to zero,
+and the settlement price is cleared.
+
+## `bid_settlement_funds_operation`
+
+This applies only to SmartCoins, not to Prediction Markets.
+
+The idea of turning the settlement fund into a short position when its
+value has increased sufficiently can easily be extended. If the value of
+the settlement fund itself is not sufficient to create a sufficiently
+collateralized short position (in terms of price feed and MCR), an
+investor could volunteer to add the required amount of collateral to the
+fund and take ownership of the resulting short position
+(collateral+debt).
 
 This operation is all that is needed empty the settlement pool and re-enable price feeds.
 It has the following payload:
@@ -85,8 +124,6 @@ It has the following payload:
    of both.
  * `additional_collateral` (asset_type): Collateral paid by the account in
    order to support the call position
- * `additional_debt` (asset_type): Debt that is paid by the account in order to reduce the
-   debt (while keeping the full settlement pool as collateral)
  * `obtain_settlement_funds` (asset_type): The amount of settlement funds the
    account is willing to obtain
 
@@ -110,6 +147,14 @@ The required checks for the operation are:
  * Are funds in the settlement pool?
  * `debt` > 0 or `collateral` > 0
  * `obtain_settlement_funds` <= `settlement_pool`
+ * the account has sufficient balance to cover `additional_collateral`
+
+If the checks are successful, a `call_order_object` belonging to the
+investor will be created or updated as described above. Then, the
+settlement price and `settlement_fund` will be cleared.
+
+The fee for this operation will be paid by the investor/recoverer. The
+fee is equal to the fee of the `call_order_update` operation.
 
 # Discussion
 
@@ -154,6 +199,22 @@ mind that
 Market participants that are willing to take risk may want to obtain a larger
 chunk of a settlement pool as it means an **instant short position**.
 
+## Feeds
+
+Re-collateralization is deliberately not restricted to the issuer of the
+globally settled bitasset. The intent here is to incentivize potential
+investors.  Effectively, during an uptrend in the value of the
+collateral, this works like a reverse auction. A higher value of the
+collateral results in a lower required amount for re-collateralization,
+i. e. the chance/risk ratio increases.  This incentive makes sense,
+because additional collateral is in the best interest of the holders of
+the settled BitAsset.
+
+This "reverse auction" ends when the BitAsset is auto-revived by
+creating a short position for the issuer. At that point, an "investor"
+could re-collateralize with zero risk, which is no longer in the
+interest of the holders.
+
 # Summary for Shareholders
 
 This proposal presents a flexible way of reviving a BitAsset that has
@@ -162,4 +223,5 @@ not need to take any risk as the proposal only offers a new way for
 market participants to (partially) revive the BitAsset.
 
 # Copyright
+
 This document is placed in the public domain.