Proposed BIP for OP_CAT

In the email, Ethan is thanked for writing up the BIP (Bitcoin Improvement Proposal) text. The sender believes that CAT (CheckTemplateVerify) would not only have the listed use cases but also open up possibilities for Bitcoin script research, allowing nontrivial experimentation before proposing dedicated opcodes. The sender mentions that whenever they discuss ideas for cool things with Bitcoin Script, about 90% of the time it ends with "we could do this if only we had CAT". They also note that CAT is simple yet valuable.The sender acknowledges the temptation to bundle other opcodes with CAT, such as rolling SHA256 opcodes to allow hashing more than 520 bytes of data. However, they believe that adding a list of opcodes would invite endless debate and that no single opcode comes close to the power of CAT. They also mention that most additions tend to be more controversial than expected.The email concludes by stating that the sender believes they should stick with "just CAT" and includes Andrew Poelstra's contact information.