docs: private final void checkCompatibility(VariableNumMap other) {
      int i = 0, j = 0;
      int[] otherNums = other.nums;
      String[] otherNames = other.names;
      Variable[] otherVars = other.vars;
      while (i < nums.length && j < otherNums.length) {
        if (nums[i] < otherNums[j]) {
          i++;
        } else if (nums[i] > otherNums[j]) {
          j++;
        } else {
          // Equal
          Preconditions.checkArgument(names[i].equals(otherNames[j]));
          Preconditions.checkArgument(vars[i].getName().equals(otherVars[j].getName()));
          i++; j++;
        }
      }
    }