18    Map<Var, unsigned int> m_indices;
 
   19    unsigned int m_n_indices = 0;
 
   23    void add(
const Var& t_var) {
 
   24        auto it = m_indices.find(t_var);
 
   25        if (it != m_indices.end()) { 
return; }
 
   26        m_indices.emplace(t_var, m_n_indices);
 
   30    [[nodiscard]] 
unsigned int get(
const Var& t_var)
 const {
 
   31        auto it = m_indices.find(t_var);
 
   32        assert(it != m_indices.end());
 
   38    [[nodiscard]] 
unsigned int n_indices()
 const { 
return m_n_indices; }