类似涉及到条件概率的问题可以用Eikosograms直观的理解。关于Eikosograms可以参考http://sas.uwaterloo.ca/~rwoldfor/papers/venn/eikosograms/paperpdf.pdf。我们学概率的时候常常使用文氏图，但是文氏图有时候会比较misleading，比如 disjoint 的事件和 independent 的事件文氏图并不容易区分。
C= 0： shaded region；
Pr( C=1 | A = 0, B = 0 ) / Pr( C=0 | A = 0, B = 0 ) = Area of T1 / Area of (S1).
基于这个定义，independence有很直观的表示。比如 S1 和 S3 的“水位”相同则表示 B 和 C 在 A=0 的条件下独立。同样的，S2 和 S4 的“水位”相同表示B 和 C 在 A=1（即A-complement） 的条件下独立。那么B 和 C 是否是 unconditionally independent 呢？这个时候我们只需要把第1列和第2列合并，第3列和第4列合并，然后看等效的“水位”是否相同即可。
Area( S1 + S2 ) / Area( T1 + T2 ) ?= Area( S3 + S4 ) / Area( T3 + T4 )
Do not believe those who try to persuade you that composition is only a cold exercise of the intellect. The only music capable of moving and touching us is that which flows from the depths of a composer’s soul when he is stirred by inspiration. There is no doubt that even the greatest musical geniuses have sometimes worked without inspiration. This guest does not always respond to the first invitation. We must always work, and a self-respecting artist must not fold his hands on the pretext that he is not in the mood. If we wait for the mood, without endeavouring to meet it half-way, we easily become indolent and apathetic. We must be patient, and believe that inspiration will come to those who can master their disinclination.
A few days ago I told you I was working every day without any real inspiration. Had I given way to my disinclination, undoubtedly I should have drifted into a long period of idleness. But my patience and faith did not fail me, and to-day I felt that inexplicable glow of inspiration of which I told you; thanks to which I know beforehand that whatever I write to-day will have power to make an impression, and to touch the hearts of those who hear it. I hope you will not think I am indulging in self-laudation, if I tell you that I very seldom suffer from this disinclination to work. I believe the reason for this is that I am naturally patient. I have learnt to master myself, and I am glad I have not followed in the steps of some of my Russian colleagues, who have no self-confidence and are so impatient that at the least difficulty they are ready to throw up the sponge. This is why, in spite of great gifts, they accomplish so little, and that in an amateur way.
Inspiration and work ethic — they ride right next to each other…. Not every day you’re gonna wake up and the clouds are gonna part and rays from heaven are gonna come down and you’re gonna write a song from it. Sometimes, you just get in there and just force yourself to work, and maybe something good will come out.