Hi All, This list has been amazinly quick and helpful so thank you all. I'm continuing my adventure through the bytecode and I have a question about the bytecodes for closures. Below is an example dump of a closure ([]) 165 <8F 10 00 1E> closureNumCopied: 1 numArgs: 0 bytes 169 to 198 169 <10> pushTemp: 0 170 <C7> send: class 171 <83 11> send: selectors 173 <83 10> send: asSortedCollection 175 <52> pushLit: WriteStream 176 <53> pushLit: String 177 <CC> send: new 178 <EA> send: on: The number on the left I will refer to as the line number to make my questions more clear. Firstly, on line 165 the closure is reporting num copied 1. What is the 1 thing that it is copying? Secondly, the send bytecode on line 171 is different to that on line 175. Is it because 175 is using a set of known selectors while 171 has to refer to a literal table? Rgs, James.