Hl!. I have problems with exercice Let and be ideals in a commutative ring . Prove that their union is a ideal if and only if or Hint please Thanks
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If y is in J but not in I and x is in I but not in J, consider x+y
Suppose i is in I but not in J. Suppose j is in J but not in I. If is an ideal, then , but implies ________ and implies _________. Any contradictions? I will admit my knowledge of commutative algebra is less than ideal these days.
Thanks