→ JASS0213 :In this case your domain can be any connected 09/30 11:27
→ JASS0213 :topological space 09/30 11:28
→ ssss50201 :謝謝您!! 09/30 20:39
f is continuous <=> preimage of an open set is open
<=> preimage of a closed set is closed
choose any subinterval J with irrational end points, then
f^{-1}(J) is open and closed, so it is either empty or R.
So obviously f is a constant.
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◆ From: 140.247.0.119
※ 編輯: JASS0213 來自: 140.247.0.119 (09/30 05:13)