1. Problem: make generator of probability 1/3 using the normal coin (1/2).

Solution
--------
Two consecutive coin flips give us 4 combinations (head-head, tail-tail,
head-tail, tail-head). We can exclude one of these combinations
(just start everything from the beginning in the case of an
unwanted combination). We get three equally probable outcomes.

1. Problem: make generator of probability 1/3 using the normal coin (1/2).

Solution
--------
Two consecutive coin flips give us 4 combinations (head-head, tail-tail,
head-tail, tail-head). We can exclude one of these combinations
(just start everything from the beginning in the case of an
unwanted combination). We get three equally probable outcomes.

2. Problem: make normal coin (1/2) from a wrong coin (unknown probability).

Solution.
---------
Probabilities of independent events are multiplied.
After two consecutive coin flips:
 - probability of tail-head P1 = x * (1 - x)
 - probability of head-tail P2 = (1 - x) * x
where x -- probability of tail.
So P1 = P2.
We can exclude head-head and tail-tail and
get two equally probable outcomes.

Add the second coin problem
Add the second coin problem

unknown probability ---> 1/2
