This is being emitted with [GCC 10.2.1](https://packages.debian.org/bullseye/g++-arm-linux-gnueabihf), in some CI jobs: i.e https://github.com/bitcoin/bitcoin/pull/25972/checks?check_run_id=12423693655, or https://github.com/bitcoin/bitcoin/pull/25972/checks?check_run_id=12423693651 (where we actually turn on all our warning flags with depends builds).
```bash
In file included from test/miniscript_tests.cpp:19:
./script/miniscript.h:1197:71: error: comparison of integers of different signs: 'typename iterator_traits<int *>::difference_type' (aka 'int') and 'const uint32_t' (aka 'const unsigned int') [-Werror,-Wsign-compare]
                    return std::count(subs.begin(), subs.end(), true) >= node.k;
                           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ^  ~~~~~~
test/miniscript_tests.cpp:346:34: note: in instantiation of function template specialization 'miniscript::Node<CPubKey>::IsSatisfiable<(lambda at test/miniscript_tests.cpp:346:48)>' requested here
        bool satisfiable = node->IsSatisfiable([](const Node&) { return true; });
                                 ^
1 error generated.
```

cc @darosior 
node(node_), expanded(exp_), state(std::move(state_)) {}
        };
        
        std::vector<StackElem> stack;
        /* Results of subtrees so far. Their order and mapping to tree nodes
         * is implicitly defined by stack. */
        std::vector<Result> results;
        stack.emplace_back(*this, 0, std::move(root_state));
        /* Here is a demonstration of the algorithm, for an example tree A(B,C(D,E),F).
         * State variables are omitted for simplicity.
         *
         * First: stack=[(A,0)] results=[]
         *        stack=[(A,1),(B,0)] results=[]
         *        stack=[(A,1)] results=[B]
         *        stack=[(A,2),(C,0)] results=[B]
         *        stack=[(A,2),(C,1),(D,0)] results=[B]
         *        stack=[(A,2),(C,1)] results=[B,D]
         *        stack=[(A,2),(C,2),(E,0)] results=[B,D]
         *        stack=[(A,2),(C,2)] results=[B,D,E]
         *        stack=[(A,2)] results=[B,C]
         *        stack=[(A,3),(F,0)] results=[B,C]
         *        stack=[(A,3)] results=[B,C,F]
         * Final: stack=[] results=[A]
         */