diff --git a/schema.t.out b/schema.t.out
new file mode 100644
index 0000000..d515fa6
--- /dev/null
+++ b/schema.t.out
@@ -0,0 +1,30 @@
+ID:	credit	promise debt
+--------------------------------
+Club:	0	+7200	-23450
+john:	7200	+0	-7200
+# Reflect john paying its bills all at once ...
+Club:	7200	+0	-23450
+john:	0	+0	0
+# Charge Club with server hosting provided by alex ...
+Club:	0	+0	-16250
+alex:	7200	+16250	0
+# Some updates and deletes that could, unless denied, destroy consistency ...
+Error: near line 274: paid is set and adjusted automatically according to added Transfer records
+Error: near line 275: Debt is involved in transfers to revoke at first
+Error: near line 276: FOREIGN KEY constraint failed
+# After revoking transactions, you are free to change or delete debts and credits ...
+Club:	7200	+0	0
+alex:	0	+0	0
+# But let's rollback that what-if excurse. This is how it currently is ...
+Club:	0	+0	-16250
+alex:	7200	+16250	0
+###################################################################
+# Now it is your turn: Study the sql code yielding the output above
+# then enter new members and let them pay the fees.
+# (PLUS: Let have one discalculia and pay too little or too much.)
+# Once the club has enough money to pay alex' hosting service,
+# update (i.e. revoke and reenter) the respective transaction.
+# Finally issue a bank transfer to alex. Hint: An outgoing transfer
+# is simply a debt charging alex' own virtual account and without
+# targetCredit (NULL). PLUS: What happens if the description of
+# the bank transfer does not contain any or only a wrong IBAN?
diff --git a/schema.t.sql b/schema.t.sql
index d0f7579..10dbbbb 100644
--- a/schema.t.sql
+++ b/schema.t.sql
@@ -1,5 +1,7 @@
 PRAGMA foreign_keys = ON;
 
+-- To understand the sql below, see the schema.sql file.
+
 INSERT INTO Account VALUES ("Club", "eV", 1, NULL), ("john", "Member", 44, NULL), ("alex", "Member", 6, "DE1234567890123456");
 
 INSERT INTO Credit VALUES (1, "Club", "2016-01-01", "Membership fees May 2016 until incl. April 2017", 0, 0),
@@ -20,19 +22,43 @@ INSERT INTO Debit VALUES ("MB1605-john", "john", 1, "2016-05-01", "Membership fe
                         ("MB1704-john", "john", 1, "2016-05-01", "Membership fee April 2017", 600, 0),
                         ("TWX2016/123", "Club", 3, "2016-01-15", "Server Hosting 2016", 23450, 0);
 
-.separator " "
-SELECT "Balance of " || ID || "'s account:", credit, debit * -1 FROM Balance WHERE ID in ("john", "Club");
-INSERT INTO Transfer (receiptId, fromCredit) VALUES ("MB1605-john", 2), ("MB1606-john", 2), ("MB1607-john", 2), ("MB1608-john", 2), ("MB1609-john", 2), ("MB1610-john", 2), ("MB1611-john", 2), ("MB1612-john", 2), ("MB1701-john", 2), ("MB1702-john", 2), ("MB1703-john", 2), ("MB1704-john", 2); 
-SELECT "Balance of " || ID || "'s account:", credit, debit * -1 FROM Balance WHERE ID in ("john", "Club");
-INSERT INTO Transfer (receiptId, fromCredit) VALUES ("TWX2016/123", 1);
-SELECT "Balance of " || ID || "'s Account:", credit, debit * -1 FROM Balance WHERE ID in ("Club", "alex");
-UPDATE Debit SET paid = 20000 WHERE receiptId="TWX2016/123";
-UPDATE Debit SET value = 20000 WHERE receiptId="TWX2016/123";
-DELETE FROM Debit WHERE receiptId="TWX2016/123"; -- *SHOULD NOT* work
+.separator "	"
+SELECT "ID:	credit	promise debt";
+SELECT "--------------------------------";
+
+SELECT ID || ":", credit, '+' || promised, debt * -1 FROM Balance WHERE ID in ("john", "Club");
+
+SELECT "# Reflect john paying its bills all at once ...";
+INSERT INTO Transfer (billId, fromCredit) VALUES ("MB1605-john", 2), ("MB1606-john", 2), ("MB1607-john", 2), ("MB1608-john", 2), ("MB1609-john", 2), ("MB1610-john", 2), ("MB1611-john", 2), ("MB1612-john", 2), ("MB1701-john", 2), ("MB1702-john", 2), ("MB1703-john", 2), ("MB1704-john", 2); 
+SELECT ID || ":", credit, '+' || promised, debt * -1 FROM Balance WHERE ID in ("john", "Club");
+
+SELECT "# Charge Club with server hosting provided by alex ...";
+INSERT INTO Transfer (billId, fromCredit) VALUES ("TWX2016/123", 1);
+SELECT ID || ":", credit, '+' || promised, debt * -1 FROM Balance WHERE ID in ("Club", "alex");
+
+SELECT "# Some updates and deletes that could, unless denied, destroy consistency ...";
+UPDATE Debit SET paid = 20000 WHERE billId="TWX2016/123";
+UPDATE Debit SET value = 20000 WHERE billId="TWX2016/123";
+DELETE FROM Debit WHERE billId="TWX2016/123"; -- *SHOULD NOT* work
+
+SELECT "# After revoking transactions, you are free to change or delete debts and credits ...";
 BEGIN TRANSACTION;
-DELETE FROM Transfer WHERE receiptId="TWX2016/123";
-UPDATE Debit SET value = 20000 WHERE receiptId="TWX2016/123";
-DELETE FROM Debit WHERE receiptId="TWX2016/123"; -- *SHOULD* work
-SELECT "Balance of " || ID || "'s Account:", credit, debit * -1 FROM Balance WHERE ID in ("Club", "alex");
+DELETE FROM Transfer WHERE billId="TWX2016/123";
+UPDATE Debit SET value = 20000 WHERE billId="TWX2016/123";
+DELETE FROM Debit WHERE billId="TWX2016/123"; -- *SHOULD* work
+SELECT ID || ":", credit, '+' || promised, debt * -1 FROM Balance WHERE ID in ("Club", "alex");
 ROLLBACK TRANSACTION;
-SELECT "Balance of " || ID || "'s Account:", credit, debit * -1 FROM Balance WHERE ID in ("Club", "alex");
+
+SELECT '# But let''s rollback that what-if excurse. This is how it currently is ...';
+SELECT ID || ":", credit, '+' || promised, debt * -1 FROM Balance WHERE ID in ("Club", "alex");
+
+SELECT '###################################################################';
+SELECT '# Now it is your turn: Study the sql code yielding the output above';
+SELECT '# then enter new members and let them pay the fees.';
+SELECT '# (PLUS: Let have one discalculia and pay too little or too much.)';
+SELECT '# Once the club has enough money to pay alex'' hosting service,';
+SELECT '# update (i.e. revoke and reenter) the respective transaction.';
+SELECT '# Finally issue a bank transfer to alex. Hint: An outgoing transfer';
+SELECT '# is simply a debt charging alex'' own virtual account and without';
+SELECT '# targetCredit (NULL). PLUS: What happens if the description of';
+SELECT '# the bank transfer does not contain any or only a wrong IBAN?';