<p style="letter-spacing:0pt;">옛날에 아주 아름답고 평온한 한 자연수 마을이 있었다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p style="letter-spacing:0pt;">그런데 어느날 그 자연수 마을에 미분귀신이 나타났다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p style="letter-spacing:0pt;">미분귀신은 마을사람들을 하나씩 미분시켜서 모조리 <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">0</span>으로 만들었다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p style="letter-spacing:0pt;">마을은 점점 황폐해져가고 이를 보다못한 촌장과 동네 사람들이 반상회를 열었다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p style="letter-spacing:0pt;">몇 시간의 토론 끝에 이웃에 있는 방정식마을에 구원을 요청하기로 했다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p style="letter-spacing:0pt;">이웃마을의 소식을 들은 방정식 마을에서는 <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">x^2</span>장군을 자연수 마을에 급파했다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p style="letter-spacing:0pt;">전투시에 수시로 자신의 모습을 바꾸는 <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">x^2</span>장군 앞에서 잠시 당황한 미분귀신<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">.... </span></p> <p style="letter-spacing:0pt;">그러나 미분귀신은 잠시 생각하더니 <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">3</span>번의 미분을 통해서 간단히 해치우고 말았다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p style="letter-spacing:0pt;">그러자 방정식마을에서는 <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">x^3</span>장군을 급파했다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p style="letter-spacing:0pt;">그러나 그 역시 미분귀신의 적수가 되기엔 역부족이었다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p style="letter-spacing:0pt;">단 <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">4</span>번의 미분에 그만 작살이 나고야 말았다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p>당황한 방정식 마을에서는 <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">x^n </span>참모총장마저 보내는 초강수를 택했으나 </p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p style="letter-spacing:0pt;">그 역시 <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">n+1 </span>번의 미분 앞에서 힘없이 무너지고 말았다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p style="letter-spacing:0pt;">이제 아무도 미분귀신의 적수가 될 수 없으리라 생각했으나<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">... </span></p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p style="letter-spacing:0pt;">방정식 나라에는 마지막 희망 <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">sinx, cosx </span>두 장군이 있었다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p style="letter-spacing:0pt;">좌 <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">sinx, </span>우 <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">cosx </span>장군이 미분귀신과 전투를 시작했다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p style="letter-spacing:0pt;">미분귀신은 적잖이 당황을 했다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p>아무리 미분을 해도 서로 모습만 바꿔가며 계속 덤비는 </p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p style="letter-spacing:0pt;"> <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">sinx, cosx </span>장군앞에서 더 이상 싸울 힘이 없었다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span> </p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p style="letter-spacing:0pt;">그러나 그 순간 미분귀신은 꾀를 내었다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p style="letter-spacing:0pt;"> <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">cosx</span>장군을 미분시켜 <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">sinx</span>장군에게 던져버린 것이다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span> </p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p style="letter-spacing:0pt;">마지막 희망이었던 두 장군은 서로 부딪쳐서 그만 자폭하고 말았다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p style="letter-spacing:0pt;">일이 이쯤 되자 방정식 마을에서는 용병을 구하느라 난리가 일고 있었다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p style="letter-spacing:0pt;">그런데 전설적인 용병이 등장했다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p style="letter-spacing:0pt;">그의 이름은 바로 <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">exponential </span>검신이었다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p style="letter-spacing:0pt;">그가 가진 <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">e^x</span>라는 무기는 미분귀신이 수백 번을 미분해도 전혀 손상되지 않았다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p style="letter-spacing:0pt;">미분귀신도 당황하기 시작했다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p style="letter-spacing:0pt;">이제 승리는 <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">exponential</span>의 것처럼 보였다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p style="letter-spacing:0pt;">하지만 끝내 그마저 미분귀신에게 끝내 패하고 말았다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p>글쎄 </p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p style="letter-spacing:0pt;">그 미분귀신이<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">... </span></p> <p style="letter-spacing:0pt;"> <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span> </p> <p style="letter-spacing:0pt;"> <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span> </p> <p style="letter-spacing:0pt;"> <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">=========== y</span>로 편미분을 해버리고 말았다 <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">=========== </span> </p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p>우리의 미분귀신이 자연함수 <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">'</span>이의 엑스승<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">'</span>을 죽이고 미분에 실증을 느낀 </p> <p style="letter-spacing:0pt;">나머지 자연수 나라를 떠났다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span>마침내 평화가 찾아온 자연수의 나라<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">.. </span></p> <p style="letter-spacing:0pt;">그러나<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">, </span>아<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">.........! </span>평화란 지속될 수 없는가<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">! </span></p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p style="letter-spacing:0pt;">이번에는 이 나라에 적분귀신이 나타나 자연수 들을 닥치는대로 적분을 하기 시작했다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p style="letter-spacing:0pt;">적분귀신은 성질도 더러운지라 엑스<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">, </span>와이 등 변수에 상관없이 무자비 하게 적분을 했다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p style="letter-spacing:0pt;">거기다가 <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">'</span>상수씨<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">'(c) </span>성질 더러운 집단을 키워나갔다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p>나라가 생긴 이래 지금까지 한 핏줄 자연수들만으로 살아온 나라에 </p> <p style="letter-spacing:0pt;">문화와 생김새가 다른 엑스<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">, </span>와이<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">, </span>상수 씨들은 많은 문제를 낳게 되었다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p>심지어 적분귀신은 엑스로 적분한 후 곧바로 와이로 적분해 버려 </p> <p style="letter-spacing:0pt;">새로운 집단인 엑스와이를 만들기도 하였다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p>이제야 평화가 오는가 했던 자연수 나라의 왕은 아연실색을 하며 </p> <p style="letter-spacing:0pt;">옆마을 다항식의 나라에 도움을 청했다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p style="letter-spacing:0pt;">그러나 다항식의 나라는 적분귀신은 자국에 도움이 된다며 이를 거절했다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p style="letter-spacing:0pt;">심지어 <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">'</span>적분귀신을 환영합니다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">' </span>하는 플랜카드를 내걸기도 하였다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p style="letter-spacing:0pt;">자연수왕은 얼마 안남은 순수 자연수들을 모아 대책회의를 열었다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p style="letter-spacing:0pt;">회의 결과 다시 미분귀신을 불러야 한다는 의견이 나왔다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p>그러나 미분귀신을 부르면 그들조차도 막대한 피해가 있기에 </p> <p style="letter-spacing:0pt;">그들 사이에도 의견이 분분했다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p style="letter-spacing:0pt;">결국 미분귀신을 부른 후 순수 자연수들만 비밀 아지트에 숨기로 하고 미분귀신을 불렀다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p style="letter-spacing:0pt;">다시 자연수 마을에 온 미분귀신<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">.! </span></p> <p style="letter-spacing:0pt;">일단 <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">'</span>상수씨<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">'</span>들을 닥치는 대로 죽이고<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">, </span>다항식들을 죽이기 시작했다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p style="letter-spacing:0pt;">거의 모든 다항식들이 죽어갈 무렵<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">, </span>미분귀신 앞에 적분귀신이 나타났다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p style="letter-spacing:0pt;"> <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">( </span>운 명 의 대 결 <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">........) </span> </p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p style="letter-spacing:0pt;">적분귀신 <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">:"</span>문제를 내어 이기는 쪽이 사라지도록 하자<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">" </span></p> <p style="letter-spacing:0pt;">미분귀신 <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">:"</span>좋다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">(</span>흐흐<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">.. </span>내겐 편미분이라는 무기가<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">..-_-+)" </span></p> <p style="letter-spacing:0pt;">그<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span>러<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span>나<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">... </span></p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p style="letter-spacing:0pt;">적분귀신이 문제로 제시한 것은 무한다변수 다항식 <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">Lim a1*a2*....*an </span>이었다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p style="letter-spacing:0pt;"> <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">-></span><span style="letter-spacing:0pt;">∽ </span> </p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p style="letter-spacing:0pt;">아무리 편미분을 해 봐도 끊임없이 쏟아지는 변수들<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">.. </span></p> <p style="letter-spacing:0pt;">미분귀신 <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">: "</span>포기다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">.. </span>너의 솜씨를 보여다오<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">..-_-;;" </span></p> <p style="letter-spacing:0pt;">적분귀신 <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">: "</span>가소로운 것<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">.. </span>에잇<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">!" </span></p> <p style="letter-spacing:0pt;">눈앞의 무한다변수다항식이 흔적도 없이 소멸되어버리는 것이 아닌가<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">... </span></p> <p style="letter-spacing:0pt;">미분귀신 <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">: "</span>어<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">.. </span>어떻게<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">?-_-;;;" </span></p> <p style="letter-spacing:0pt;">적분귀신 <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">: "......." </span></p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p style="letter-spacing:0pt;">그렇다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">... </span></p> <p style="letter-spacing:0pt;">적분귀신은 다항식을 <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">0</span>에서 <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">0</span>까지 정적분해 버렸던 것이다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">...-_-;; </span></p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p style="letter-spacing:0pt;">적분귀신은 정말 대단했다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p>승승장구를 치던 적분귀신에게 대적할만한 상대가 </p> <p style="letter-spacing:0pt;">자연수 마을에서는 더 이상 존재하지 않았다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p>여지없이 무너진 미분귀신은 함께 힘을 합하여 </p> <p style="letter-spacing:0pt;">적분귀신을 물리칠 동업자를 찾아 나섰다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p>정수마을<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">, </span>유리수마을<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">, </span>실수마을<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">, </span>심지어 </p> <p style="letter-spacing:0pt;">그 복잡하다는 복소수<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">(complex number)</span>마을까지<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">... </span></p> <p style="letter-spacing:0pt;">그러나 미분귀신은 더 이상 동업자를 찾을 수 없는 듯 했다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p style="letter-spacing:0pt;"> <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">"</span>수의 마을에서는 도저히 찾을 수 없는 것인가<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">?..." </span> </p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p style="letter-spacing:0pt;">자포자기한 미분귀신 앞에 펼쳐진 광경은 정말 놀라운 광경이었다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p>실수 및 복소수 마을에서 연속<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">(continuous)</span>인 함수들이 </p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p style="letter-spacing:0pt;">어떤 놈에게 여지없이 터져서는 산산 조각이 나는 것이었다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p style="letter-spacing:0pt;"> <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">"</span>저놈이닷<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">!" </span>미분귀신이 외쳤다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span> </p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p style="letter-spacing:0pt;">자세히 보니 그놈은 델타함수<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">(delta function)</span>였다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p>연속함수들을 <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">sampling</span>을 통해 </p> <p style="letter-spacing:0pt;">이산<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">(discrete)</span>함수로 만들고 있었던 것이다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p style="letter-spacing:0pt;">며칠 후<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">... </span></p> <p>자연수 마을로 돌아온 미분귀신은 </p> <p style="letter-spacing:0pt;">델타함수를 적분귀신 앞에 내놓았다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p>적분귀신은 자신의 비장의 무기인 </p> <p style="letter-spacing:0pt;"> <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">0</span>에서 <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">0</span>까지 정적분을 사용했다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span> </p> <p style="letter-spacing:0pt;">그러나 델타함수는 사라지지 않고 <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">1</span>을 남겼다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p style="letter-spacing:0pt;">델타함수는 정말 대단했다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p style="letter-spacing:0pt;">특이하게도 <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">0(-0)</span>에서 <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">0(+0)</span>까지 정적분을 하면 <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">1</span>이 되는 것이었다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p>순간 당황한 적분귀신은 정신을 가다듬고 </p> <p style="letter-spacing:0pt;">다시 <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">0</span>에서 <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">0</span>까지 정적분을 시도했다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p style="letter-spacing:0pt;">그러자 <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">1</span>이 사라졌다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p style="letter-spacing:0pt;">이때 나선 미분귀신은 델타함수를 무한번 미분해주기 시작했다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p>적분귀신이 아무리 아무리 <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">0</span>에서 <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">0</span>까지 정적분을 시도해도 </p> <p style="letter-spacing:0pt;">미분을 통해 계속 델타함수의 변종들이 나타나는 것이었다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p style="letter-spacing:0pt;">적분귀신은 드디어 두 손 두 발<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">, </span></p> <p style="letter-spacing:0pt;">아니 두 인티그랄<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">(integral)</span>을 다 들고 말았다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p style="letter-spacing:0pt;">미분귀신과 델타함수의 연합전선은 정말 대단했다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p>그러나 잠시잠깐 그들이 한눈을 판 사이에 </p> <p style="letter-spacing:0pt;">그들은 사라지고 말았다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p style="letter-spacing:0pt;"> <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">"</span>무슨 일이지<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">...?" </span>적분귀신이 고개를 들었다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span> </p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p style="letter-spacing:0pt;"> <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">... </span> </p> <p style="letter-spacing:0pt;"> <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">... </span> </p> <p style="letter-spacing:0pt;"> <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">... </span> </p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p style="letter-spacing:0pt;">그 거대한 몸짓<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p>그는 말 한마디로 모든 것을 사라지게 할 수 있는 </p> <p style="letter-spacing:0pt;">거의 신적인 존재였다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p>그는 바로 </p> <p style="letter-spacing:0pt;"> <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">'</span>정의<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">(definition)</span>귀신<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">'</span>이었다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span> </p> <p>미분귀신과 델타함수가 열심히 <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">ally</span>를 해도 </p> <p>마지막에 정의귀신이 <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">"= 0" </span>한마디면 </p> <p style="letter-spacing:0pt;">끝나는 것이었다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p style="letter-spacing:0pt;">과연 정의귀신을 대적할 자가 이 세상에 존재할런지<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p> <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">.. </span>바야흐로 중원의 미분 귀신과 적분 귀신에 의한 전국 시대는 </p> <p style="letter-spacing:0pt;">정의 귀신이라는 새로운 귀신의 등장으로 인하여 새로운 국면에 접어들게 되었다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p style="letter-spacing:0pt;">정의 귀신의 활약은 대단했다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p style="letter-spacing:0pt;">정의 귀신이 지나간 자리는 모두 <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">0</span>으로 황폐화 되고<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">, </span></p> <p style="letter-spacing:0pt;">모든 마을 사람은 정의 귀신이 나타났다는 소문만 나도 무서워서 꼼짝을 못하게 되었다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p style="letter-spacing:0pt;">그러던 어느날<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">, </span>정의 귀신은 한 작은 마을을 지나게 된다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p style="letter-spacing:0pt;">정확하게 말하자면<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">, </span>그 마을의 규모를 파악할 수 없었지만<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">, </span></p> <p style="letter-spacing:0pt;">겉보기에는 별 것 아닌듯하게 보이는 마을이었다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p style="letter-spacing:0pt;">하지만<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">.. </span>문제는<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">.. </span></p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p style="letter-spacing:0pt;">마을 사람들이 정의 귀신이 마을에 도착했는데도 별다른 반응이 없었던 것이다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. -_-;; </span></p> <p>그동안 모든 사람들에게 공포의 대상이었던 자신이 </p> <p style="letter-spacing:0pt;">이렇게 무시당하는 것에 정의 귀신은 황당함 이전에 분노가 끓어올랐다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p style="letter-spacing:0pt;">마침 굉장히 어리바리해 보이는 한 꼬마가 눈에 띄었다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p style="letter-spacing:0pt;">정의 귀신은 자신의 힘을 과시하겠다는 듯<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">, "= 0"</span>을 외쳤다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span>그러나 그 어리바리해 보이는 꼬마는 눈 깜짝 하지 않고<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">, </span>대뜸 이렇게 반문하는 것이었다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p style="letter-spacing:0pt;"> <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">"</span>아저씨<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">, </span>그건 <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">95%</span>의 신뢰 구간에서는 채택될지 몰라도 저는 유의수준이거든요<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span>딴 데 가서 알아봐요<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">." </span> </p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p style="letter-spacing:0pt;">정의 귀신으로서는 알 수 없는 방어였지만<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">, </span>굉장히 자존심이 상했다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p style="letter-spacing:0pt;">무슨 공격을 해도 공격 자체에 대한 집합을 기각해 버리는 그 꼬마한테는 먹혀들지 않는 것이었다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p style="letter-spacing:0pt;">화가 난 정의 귀신은 옆에서 미소를 짓고 있는 청년에게 화풀이성 공격을 하였다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p style="letter-spacing:0pt;">하지만<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">, </span>그 청년은 정의 귀신이 공격할 때마다 계속해서 실수<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">(Real number)</span>를 만들어내는 것이 아닌가<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">? </span></p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p style="letter-spacing:0pt;">정의 귀신은 이해할 수 없었다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p style="letter-spacing:0pt;">왜 사라지기는 커녕 계속해서 실수를 만들어내는 것인가<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">? </span></p> <p style="letter-spacing:0pt;">정의 귀신은 그 청년에게 도대체 정체가 무엇이며<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">, </span>여기는 어디인가를 묻지 않을 수가 없었다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p style="letter-spacing:0pt;">청년은 대답했다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span></p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p style="letter-spacing:0pt;"> <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">"</span>저는 확률 함수<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">(Probability function)</span>라고 합니다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span>당신이 어떠한 정의를 내리건 간에 그에 따른 확률을 계산합니다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">." </span> </p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p style="letter-spacing:0pt;"> <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">"</span>이럴수가<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">.. " </span> </p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p style="letter-spacing:0pt;"> <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">"</span>이 마을은 <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">'</span>확률과 통계<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">'</span>라는 연합 마을입니다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span>이 마을 사람들은 당신과 같이 정의내리기 좋아하는 족속들에게 진실을 알려주지요<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">." </span> </p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p style="letter-spacing:0pt;"> <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">"</span>그렇군<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span>그래서 나의 공격이 전혀 먹혀들지 않았던 것이군<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span>한 가지만 더 묻겠다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span>왜 그런 힘을 지니고 있으면서도 세상을 지배하려 하지 않는 것이지<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">?" </span> </p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p style="letter-spacing:0pt;"> <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">" </span>저희가 가진 힘은 시계열이란 마을 사람들이 가진 힘에 비교하면 아무 것도 아니기 때문입니다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span>그 마을 사람들은 미래를 예언하고<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">, </span>또한 원하는 미래를 실현시키는 무서운 능력을 갖고 있지요<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span>시계열 마을 뿐 만이 아닙니다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span>저 길로 계속 가면 또 어떤 마을이 있는지는 시계열 마을 사람들도 극소수만이 알고 있습니다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">. </span>소문에는 넓이는 유한한데 둘레는 무한해서 그 형체를 알 수 없는 프랙탈<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">(Fractal)</span>이라는 마을이 제일 가까이 있다고 합니다<span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">." </span> </p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p style="letter-spacing:0pt;"> <span lang="en-us" style="font-family:'바탕';letter-spacing:0pt;">"..." </span> </p> <p> <span style="font-family:'바탕';"> </span></p><p></p> <p> <span style="font-family:'한컴바탕';"> </span></p><p></p>