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**     used in other ERFA functions:
**
**     . eraXy06  contains the polynomial parts of the X and Y series.
**
**     . eraS06  contains the polynomial part of the s+XY/2 series.
**
**     . eraPfw06  implements the series for the Fukushima-Williams
**       angles that are with respect to the GCRS pole (i.e. the variants
**       that include frame bias).
**
**  4) The IAU resolution stipulated that the choice of parameterization
**     was left to the user, and so an IAU compliant precession
**     implementation can be constructed using various combinations of
**     the angles returned by the present function.
**
**  5) The parameterization used by ERFA is the version of the Fukushima-
**     Williams angles that refers directly to the GCRS pole.  These
**     angles may be calculated by calling the function eraPfw06.  ERFA
**     also supports the direct computation of the CIP GCRS X,Y by
**     series, available by calling eraXy06.
**
**  6) The agreement between the different parameterizations is at the
**     1 microarcsecond level in the present era.
**
**  7) When constructing a precession formulation that refers to the GCRS
**     pole rather than the dynamical pole, it may (depending on the
**     choice of angles) be necessary to introduce the frame bias
**     explicitly.
**
**  8) It is permissible to re-use the same variable in the returned
**     arguments.  The quantities are stored in the stated order.
**
**  References:
**
**     Capitaine, N., Wallace, P.T. & Chapront, J., 2003,
**     Astron.Astrophys., 412, 567
**
**     Hilton, J. et al., 2006, Celest.Mech.Dyn.Astron. 94, 351
**
**  Called:
**     eraObl06     mean obliquity, IAU 2006
**
**  Copyright (C) 2013-2020, NumFOCUS Foundation.
**  Derived, with permission, from the SOFA library.  See notes at end of file.
*/
{
   double t;


/* Interval between fundamental date J2000.0 and given date (JC). */
   t = ((date1 - ERFA_DJ00) + date2) / ERFA_DJC;

/* Obliquity at J2000.0. */

   *eps0 = 84381.406 * ERFA_DAS2R;

/* Luni-solar precession. */

   *psia = ( 5038.481507     +
           (   -1.0790069    +
           (   -0.00114045   +
           (    0.000132851  +
           (   -0.0000000951 )
           * t) * t) * t) * t) * t * ERFA_DAS2R;

/* Inclination of mean equator with respect to the J2000.0 ecliptic. */

   *oma = *eps0 + ( -0.025754     +
                  (  0.0512623    +
                  ( -0.00772503   +
                  ( -0.000000467  +
                  (  0.0000003337 )
                  * t) * t) * t) * t) * t * ERFA_DAS2R;

/* Ecliptic pole x, J2000.0 ecliptic triad. */

   *bpa = (  4.199094     +
          (  0.1939873    +
          ( -0.00022466   +
          ( -0.000000912  +
          (  0.0000000120 )
          * t) * t) * t) * t) * t * ERFA_DAS2R;

/* Ecliptic pole -y, J2000.0 ecliptic triad. */

   *bqa = ( -46.811015     +
          (   0.0510283    +
          (   0.00052413   +
          (  -0.000000646  +
          (  -0.0000000172 )
          * t) * t) * t) * t) * t * ERFA_DAS2R;

/* Angle between moving and J2000.0 ecliptics. */

   *pia = ( 46.998973     +
          ( -0.0334926    +
          ( -0.00012559   +
          (  0.000000113  +
          ( -0.0000000022 )
          * t) * t) * t) * t) * t * ERFA_DAS2R;

/* Longitude of ascending node of the moving ecliptic. */

   *bpia = ( 629546.7936      +
           (   -867.95758     +
           (      0.157992    +
           (     -0.0005371   +
           (     -0.00004797  +
           (      0.000000072 )
           * t) * t) * t) * t) * t) * ERFA_DAS2R;

/* Mean obliquity of the ecliptic. */

   *epsa = eraObl06(date1, date2);

/* Planetary precession. */

   *chia = ( 10.556403     +
           ( -2.3814292    +
           ( -0.00121197   +
           (  0.000170663  +