Pushdown Automaton to accept all strings such that no prefix has more 1’s than 0’s
If we have a word, $w=a_1a_2\dots a_n$ where the $a_i$ are characters from the underlying alphabet, then the prefixes of $w$ are the empty word, $\epsilon$, and the words $a_1$, $a_1a_2$, $a_1a_2a_3$, ..., $a_1a_2\dots a_{n-1}a_n$. In informal terms, the prefixes of a word consist of all left-hand segments of the word.