Jgarzik, how does that design enforce two-way pegging?

Gmaxwell, what would the new opcodes be? Would they verify that a program in C faithfully executed as described in SNARKs for C: Verifying Program Executions Succinctly and in Zero Knowledge, which was mentioned in this CoinWitness thread: https://bitcointalk.org/index.php?topic=277389.0    ?

Is it possible to implement sidechains for Bitcoin without changing Bitcoin? i.e. relying on the current OP codes?

I'd appreciate any thoughts, thanks!