Gravitational Attraction Figure 2.6

[BotiKis]

It's not really an issue but it bugs me every time i see it.
There are two Vectors Fg pointing towards each other from the two masses.
One of them should be -Fg since there are not the same! Even if it may confuse some beginners, it should get clear as they read and understand your n-body code.
Or simply call them Fm1 and Fm2.

[shiffman]

Moved: https://github.com/shiffman/The-Nature-of-Code/issues/96