struct PK_FACE_set_pair_s
    {
    int          n_faces1;   --- Number of faces in first set
    PK_FACE_t   *faces1;     --- First set of faces
    int          n_faces2;   --- Number of faces in second set
    PK_FACE_t   *faces2;     --- Second set of faces
    PK_BODY_t    sheet;      --- Sheet to be trimmed
    PK_LOGICAL_t sheet_pretrimmed;
                             --- Whether sheet is already trimmed
    };
typedef struct PK_FACE_set_pair_s PK_FACE_set_pair_t;





This data structure contains a pair of sets of faces and its
corresponding neutral sheet.




The faces in faces1 and faces2 will specify the way the sheet body
given in the field sheet should be trimmed.  Each face set must
contain at least one face and all the faces must belong to the same
solid body.  sheet may contain any number of faces but all the faces
must have the same surface. sheet may not be PK_ENTITY_null.

The value of the logical field sheet_pretrimmed indicates whether
the neutral sheet is to be trimmed.  If it is PK_LOGICAL_true, then
trimming of the neutral sheet is not required but the definition of
the face set pair is required to specify how adjacent neutral sheets
are to be trimmed.  If the value of sheet_pretrimmed is
PK_LOGICAL_false, then the neutral sheet is required to be trimmed.