Remarks on retracts of polynomial rings in three variables in any characteristic
摘要
Let A be a retract of the polynomial ring in three variables over a field k. It is known that if char (k) = 0 or tr.degkA ≠ 2, then A is a polynomial ring. We give some sufficient conditions for A to be the polynomial ring in two variables over k when char (k) > 0 and tr.degkA = 2.