code: public BigDecimal modelCount(final BDD bdd, final int unimportantVars) {
      return modelCount(bdd).divide(BigDecimal.valueOf((int) Math.pow(2, unimportantVars)));
    }
docs: Returns the model count of a given BDD with a given number of unimportant variables.
  @param bdd             the BDD
  @param unimportantVars the number of unimportant variables
  @return the model count