$\underline{\text { Rubanov I.S. }}$

Microcalculator MK-97 can perform only three operations on numbers stored in memory:

1) check if two selected numbers are equal,
2) add selected numbers,
3) find the roots of the equation $x^{2}+a x+b=0$ for selected numbers $a$ and $b$, or display a message if there are no roots.

The results of all actions are stored in memory. Initially, the memory contains a single number $x$. How can one use the MK-97 to determine if this number is equal to one?
By adding $x$ to itself, we get $2x$. We compare $x$ and $2x$. If they are equal, then $x=0$. Otherwise, we find the roots of the equation $y^{2}+2xy+x=0$. The discriminant of this equation is $4(x^{2}-x)$, so the roots are equal if and only if $x=1$.