diff --git a/Comments:BIP-0199.md b/Comments:BIP-0199.md
index 3fe06f6..c5ab9fd 100644
--- a/Comments:BIP-0199.md
+++ b/Comments:BIP-0199.md
@@ -1 +1,17 @@
-In the scripts in this proposal, pubkey hashes are used for the buyer and seller; is there an advantage over using just pubkeys? I can see only a disadvantage, i.e. increased space usage in redeeming.
\ No newline at end of file
+In the scripts in this proposal, pubkey hashes are used for the buyer and seller; is there an advantage over using just pubkeys? I can see only a disadvantage, i.e. increased space usage in redeeming.
+
+==========
+
+Should directly use pubkey, instead of pubkey hash. Using pubkey hash will require more witness space for no benefit. The following script should consume the minimal space:
+
+    [HASHOP] <digest> OP_EQUAL
+    OP_IF
+        <seller pubkey>            
+    OP_ELSE
+        <num> [TIMEOUTOP] OP_DROP <buyer pubkey>
+    OP_ENDIF
+    OP_CHECKSIG
+
+~~Johnson Lau
+
+==========