text: #ifndef STAN_MATH_REV_SCAL_FUN_IS_NAN_HPP
  #define STAN_MATH_REV_SCAL_FUN_IS_NAN_HPP
  
  #include <stan/math/rev/core.hpp>
  #include <stan/math/prim/scal/fun/is_nan.hpp>
  #include <stan/math/prim/scal/fun/constants.hpp>
  
  namespace stan {
  namespace math {
  
  /**
   * Returns 1 if the input's value is NaN and 0 otherwise.
   *
   * Delegates to <code>is_nan(double)</code>.
   *
   * @param v Value to test.
   *
   * @return <code>1</code> if the value is NaN and <code>0</code> otherwise.
   */
  inline bool is_nan(const var& v) { return is_nan(v.val()); }
  
  }  // namespace math
  }  // namespace stan
  #endif
  