There were question in exam, which I understood very close to correct, thus absolutely wrong.

Roughly translated: “*Define real axis ℝ Lebesque outermeasure on ℝ² surface*“

Lets get into it. Bit intuitively first.. Suppose we have segment of a line* (a,b)*

segment (*s*) itself can be expressed as

Actually, lets forget about *s*, lets consider without segments, ie

Then outer measure can be expressed as union of open sets:

for all

Where intervals are:

Thus length of intervals are from one integer to another – ,.. all integers

Height of intervals are

Ie , where biggest height is , which is quater of epsilon.

Therefore

or shorter: and for all

It is obvious from here

This article was inspired by **Margarita**.