A grammar $G$ is called ambiguous if there is a string $\omega$ in the language generated from the grammar $L(G)$ such that it has at least two different abstract syntax trees $\operatorname{AST}_G(\omega)\neq \operatorname{AST}^\prime_G(\omega).$
If for all $\omega\in L(G)$ there are unique abstract syntax trees $\operatorname{AST}_G(\omega),$ the grammar is called unambiguous.
Examples: 1