code: function satisfiable (clause, model) {
    // If every variable is false, then the clause is false.
    if (clause.every(function (v) { return resolve(v, model) === false; }))
      return false;
    // If any variable is true, then the clause is true.
    if (clause.some(function (v) { return resolve(v, model) === true; }))
      return true;
  
    // Otherwise, we don't know what the clause is.
    return undefined;
  }
docs: ### satisfiable Determines whether a clause is satisfiable given a certain model.