▁There ▁is ▁also ▁an ▁inclusion ▁of ▁she aves ▁ ▁This ▁furn ishes ▁a ▁canonical ▁element ▁of ▁ ▁namely , ▁the ▁image ▁of ▁the ▁global ▁section ▁ 1 . ▁This ▁is ▁called ▁the ▁canonical ▁section ▁and ▁may ▁be ▁denoted ▁s D . ▁While ▁the ▁canonical ▁section ▁is ▁the ▁image ▁of ▁a ▁now here ▁van ishing ▁rational ▁function , ▁its ▁image ▁in ▁ ▁van ishes ▁along ▁D ▁because ▁the ▁transition ▁functions ▁van ish ▁along ▁D . ▁When ▁D ▁is ▁a ▁smooth ▁Cart ier ▁divis or , ▁the ▁c ok ernel ▁of ▁the ▁above ▁inclusion ▁may ▁be ▁identified ; ▁see ▁# Cart ier ▁divis ors ▁below . ▁ ▁Assume ▁that ▁X ▁is ▁a ▁normal ▁integral ▁separated ▁scheme ▁of ▁finite ▁type ▁over ▁a ▁field . ▁Let ▁D ▁be ▁a ▁We il ▁divis or . ▁Then ▁ ▁is ▁a ▁rank ▁one ▁ref lex ive ▁she af , ▁and ▁since ▁ ▁is ▁defined ▁as ▁a ▁sub she af ▁of ▁ ▁it ▁is ▁a ▁fraction al ▁ideal ▁she af ▁( see ▁below ). ▁Con vers ely , ▁every ▁rank ▁one ▁ref lex ive ▁she af ▁corresponds ▁to ▁a ▁We il ▁divis or : ▁The ▁she af ▁can ▁be ▁restricted ▁to ▁the ▁regular ▁loc us , ▁where ▁it ▁becomes ▁free ▁and ▁so ▁corresponds ▁to ▁a ▁Cart ier ▁divis or ▁( ag ain , ▁see ▁below ), ▁and ▁because ▁the ▁singular ▁loc us ▁has ▁cod im ension ▁at ▁least ▁two , ▁the ▁closure ▁of ▁the ▁Cart ier ▁divis or ▁is ▁a ▁We il ▁divis or . ▁ ▁Div is or ▁class ▁group