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exercises.md

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 88. [Optical fiber](optical_fiber.md) cabels mustn't be bent too much -- one reason for this is that the fibers inside might crack, but another reason is related to the physics of how the light travels inside. What is this effect of optics called and why does it limit the bend radius?
 89. We know that an [ellipse](ellipse.md) is a set of points in 2D plane that have constant sum of [distances](distance.md) to some two given points that are called *focal points*. What if we instead consider a taxicab distance (computed as distance alongside X axis plus distance alongside Y axis)? Consider the constant sum of distances to always be set higher than the taxicab distance of the two focal points. What shape will we get? Just describe the shape and intuitively show why it looks like that.
 90. What does [Turing tarpit](turing_tarpit.md) mean?
-91. Did you enjoy this quiz?
+91. =fgtnmtg qlcowj jakju lm vglcnr gjv dm gocl gjv qk vcjU
+92. Did you enjoy this quiz?
 
 ### Answers
 
@@ -285,7 +286,8 @@ Bear in mind the main purpose of this quiz is for you to test your understanding
 88. Total internal refraction -- light travelling in the fibers bounces off of the walls of the fiber, but in order to bounce (be reflected) when it hits the boundary it must hit it under an angle that's smaller than so called critical angle which is calculated from the indices of refraction of the fiber and the material outside of it. If the cable was bent too much, light could hit the boundary under and angle close to perpendicular and by this it would escape to the outside medium.
 89. Kind of octagon but with unevenly long sides; a rectangle with bevelled corners, i.e. two horizontal sides, two vertical sides, two 45 degree walls and two 135 degree walls. We can imagine taxicab distance from given point like sort of a diamond, it creates 4 quadrants around the point, in each the distance increases linearly in diagonal direction -- regions of constant distance here form 45 degree angled squares. Boundaries between these quadrants form a cross of infinite size. Taking two different points these two crosses will overlap and form 9 regions (draw it): top-left, top-middle, top-right, middle-left etc. Examining each of the regions we will find that it either keeps the increasing direction the same (if both overlaid directions are the same) or that some principal direction cancels out and leave the sum increasing only in one principal direction -- basically we find that in each of those regions the sum increases linearly in one of 8 directions separated by 45 degrees (except for the middle region where the sum is constant). It's also clear the heightmap has to stay continuous as both of the summed functions are continuous. From all this we can deduce the shape basically.
 90. It's a [Turing complete](turing_complete.md) system (typically a [programming language](programming_language.md)) that's however extremely hard to use for any practical programming, i.e. it can be seen as a programming language in which it is theoretically possible to program anything (anything programmable in any other language) but practically it's impossible to program anything significant because of the complicated nature of that language. This terms is related to [esoteric languages](esolang.md).
-91. yes
+91. [Earth](earth.md) or jvpcG. The cipher reverses the ASCII string and xors every byte (that's not a space) with 0x02 (i.e. flips the second lowest bit) -- don't bitch too much about this being too arbitrary, you can notice the string is reversed by the last character being uppercase and the first one being special char (?), then you can kind of recognize the words as the encoded chars are close to their decoded versions and the lengths of the words also hint on the words (for example a question is quite likely to start with "What").
+92. yes
 
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