How do pencil erasers work?

Is the triple <pencil, paper, eraser> rightly regarded as a miracle?

• Edited question details after a discussion with : Should we expect, a priori from the laws of physics, the existence of a triple of materials with the properties and relations that pencils, papers, and erasers have? I ask this because the pencil/paper/eraser system doesn't seem to be particularly robust.  You can use a pencil to write on wood, cardboard, or certain fabrics, but it doesn't erase very easily.  You can write on a tissue with a pen, but not with a pencil.  You can erase pencil, but not ink.  You can write with chalk on a chalkboard, but that erases too easily -- you couldn't write some notes on a small chalkboard, throw it in your backpack, and read them later.  A cuneiform tablet has the same problem, unless you bake it, at which point you can't erase any more. So you have three materials with a very specific relation to one another.  You don't seem to be able to perturb any of the three at all and still maintain these basic properties.  The only other system I can think of with all these properties is computer memory, and that's a far more sophisticated system. As such, it sounds like the existence of three such things with such a relation might be a complete fluke -- something that wouldn't exist at all if the world we lived in was even slightly different. One potential answer, of a negative variety, would be something along the lines of "obviously this system would exist, but in general putting that many constraints on a few materials results in problems that we don't in general know how to solve.  For instance, here's a similar-sounding problem that hasn't been solved." A potential positive answer could be something like, "Oh, yeah, give me any material out there -- tissue paper, foam rubber, wool -- and I'll come up with something that writes on it and something that erases that.  It's a simple matter of finding something whose index of .... is ...." Original question details: Imagine an alternate reality where we have similar knowledge of science, but do not know about the pencil, paper, or erasers.  Perhaps we've simply used cuneiform and clay tablets for everything, or have a rigidly formalized oral tradition; who knows? Now suppose I walk in and tell you the following: "I've invented three new materials that work together in a very interesting way.  This is paper, which I can make into thin sheets that hang together fairly well, but can be folded, rolled up into a tube, etc.  Not so interesting, I agree, but wait.  This is a pencil.  It allows me to make markings on the paper which will persist even if the paper is crumpled up, rolled up, folded, shaken, brushed up against, etc.  Again, not so crazy, because that's just the same thing that ink does.  However -- and here's the kicker! -- this is an eraser.  If I rub the eraser over the paper, it will remove the pencil markings from the paper, but leave the paper almost completely intact!" Note that the only other system I can think of that satisfies all these properties is magnetic tape storage, and that requires much more sophisticated machinery and isn't as robust to damage. With our general knowledge of physics and materials, but no specific knowledge that things such as pencils and erasers existed, should we expect that such a system could be designed with such crude parts, or is this a remarkable coincidence?

• Answer:

  Miracles don't exist, all those three items were invented by humans, great and very useful inventions though Update... I would probably say hold on while make a note of your idea on my iClay tablet.