One of the oldest instruments or tools man has made amongst such basic inventions like the axe and fire is the ski. Archeologists have found ancient skis in the marshes preserved by water. The ski was extremely important object for man during the winter when large amounts of snow hindered the free motion in the woods. Without the ski man would have drown or sink deep in the snow.

The first skis were made of wood, the natural material for our ancestors. The size and forms developed as times went by, in the beginning there were two different sizes of ski. The long one was used to slide; the other short one was used to push speed. A stick or lance was used to push speed by hands and hunt game. Hence the object is the snow, the tool the ski, the field the weight of man.

A natural material to protect the ski over the years was tar, a modification of wood. Hence we have the Su-Field where ski is attacked by a chemical field, and the solution is of course to add a substance, which should at the best be a modification of the substance. So was the case, as we know that tar is made of wood.
Tar was also useful for providing sliding effect as well as grip. Thus tar was elementary wax which possessed two mutually contradictory properties, one of grip the other of slide. However neither was good enough, so men invented to use tallow for sliding. Tallow was spread under the longer ski; the shorter was merely tarred without any tallow.
The ski was originally most likely flat, only the front was turned upwards to help keeping afloat. The modern cross-country skis are made of plastic and of equal length and curved in the middle plus turned-up toe.

The skiing techniques and the ski are combined in a way to provide two functions: one of sliding, the other for pushing additional speed and to proceed. Here we have two Operational Times, OT, and Operational Zones, OZ.

In the former case of sliding, the OT1, the OZ1 will be the fore and tail of the ski. In the latter of pushing more speed, during the OT2, the OZ2 is the middle of the ski. For sliding purposes a sliding wax is spread over the OZ1.

For providing grip or friction during OT2, a special grip wax is applied on the middle or OZ2. So simple!

We have clearly a Physical Contradiction, PC, the wax should slide, and the wax should not slide, but grip. We know the solution of PC to be separation in time (OT1 and OT2), separation in space (OZ1 and OZ2), and even separation in structure (the form of the ski).

The latter requires some additional information. When choosing your skis you must take a pair of skis, which are curved enough, in the middle not to touch the ground. This applies when you are standing your weight equally distributed on both skis. This is for the sliding phase. On the other hand the ski should go flat and the wax grip the track when you are moving your weight totally on the other ski and simultaneously pushing downwards and backwards to give speed. Then you make it in turns, left, right, left, right (This is something like giving you a letter course in riding bicycle!).
The lesson above applies only to conventional cross-country style ski. The new 'free' style uses skis, which are shorter and both using only sliding wax. The technique is called also 'skating' reminding us on skating on ice. But that is another story.
In the spirit of Altshuller, please use this example free!