Zariski-Nagata's purity theorem
20/05/2014 18:55
X is normal integral scheme.
Y is regular integral scheme.
f : X -> Y is quasi-definite and dominant morphism.
Subset Z contained X is defined to f's non-etale part.
Z is closwd set and Z is not equal to X, 0.
When the upper conditions are satisfied, Z is pure codimension 1 over X.