Min value in custom field not checked

Hello,
I set up a custom field of type Number with max value 10, min value 0, step 1 and default 0.
At registration, it is possible to select a negative value, as you can see from the attached screen shot. A negative selection should not be allowed, I guess, as it is the case for the in the positive direction.

The introduction of a value greater than the max value is checked by and additional formula.
How could I extend the formula to check the introduction of a value less than the lower bound?

Sincerely,
Leon