An engineer, a physicist and a mathematician were asked to hammer a nail into a wall.

The engineer went to build a Universal Automatic Nailer – a device able to hammer every possible nail into every possible wall.

The physicist conducted series of experiments on strength of hammers, nails, and walls and developed a revolutionary technology of ultra-sonic nail hammering at super-low temperature.

The mathematician generalized the problem to an N dimensional problem of penetration of a knotted one dimensional nail into an N-1 dimensional hyper-wall. Several fundamental theorems are proved. Of course, the problem is too rich to suggest a possibility of a simple solution, even the existence of a solution is far from obvious.