For player that want to use a stack combinator inside a compact circuit processor, you can install https://mods.factorio.com/mod/stack4cc

🎉🎉🎉

Actually, i've found a minimalistic design for SC using 5 combinators (6 for synchronization, 9 for the "default" case) and some constant combinators:

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

Nice setup. Mine is more classic and covers all functions of stack combinator. Maybe you may have an overflow problem with ^2