# What strings can be used in pumping lemma?

I just got my homework back after correction and I can't figure out why this questions was wrong.

I need to say if I can prove that the language ${L=\{w\in \{0,1\}|w}$ has more 0's than 1's} is not regular with a given string.

Both $0^p1^p$ and $0^{p+1}1^p$ were options and I said both could be used, but the correct answer was that only $0^{p+1}1^p$ could be used?

I thought that if $s=0^{p}1^p=xyz$ then $xy^0z$ would make it so that there would be less than $p$ zeros since $y>0$.

Is my logic wrong or was it a bad correction? Thanks!

The string $0^p1^p$ is not an element of the language $L$ (it does not have more $0$s and $1$s). The pumping lemma only applies to strings that are actually in the language!