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- Automata Theory Introduction
- Deterministic Finite Automaton
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- NDFA to DFA Conversion
- DFA Minimization
- Moore & Mealy Machines
- Classification of Grammars
- Introduction to Grammars
- Language Generated by Grammars
- Chomsky Grammar Classification
- Regular Grammar
- Regular Expressions
- Regular Sets
- Arden's Theorem
- Constructing FA from RE
- Pumping Lemma for Regular Grammar
- DFA Complement
- Context-Free Grammars
- Context-Free Grammar Introduction
- Ambiguity in Grammar
- CFL Closure Properties
- CFG Simplification
- Chomsky Normal Form
- Greibach Normal Form
- Pumping Lemma for CFG
- Pushdown Automata
- Pushdown Automata Introduction
- Pushdown Automata Acceptance
- PDA & Context Free Grammar
- PDA & Parsing
- Turing Machine
- Turing Machine Introduction
- Accepted & Decided Language
- Multi-tape Turing Machine
- Multi-Track Turing Machine
- Non-Deterministic Turing Machine
- Semi-Infinite Tape Turing Machine
- Linear Bounded Automata
- Decidability
- Language Decidability
- Undecidable Language
- Turing Machine Halting Problem
- Rice Theorem
- Post Correspondence Problem
- Automata Theory Useful Resources
- Automata Theory - Quick Guide
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- Automata Theory - Discussion
Ambiguity in Context-Free Grammars
If a context free grammar G has more than one derivation tree for some string w ∈ L(G), it is called an ambiguous grammar. There exist multiple right-most or left-most derivations for some string generated from that grammar.
Problem
Check whether the grammar G with production rules −
X → X+X | X*X |X| a
is ambiguous or not.
Solution
Let’s find out the derivation tree for the string "a+a*a". It has two leftmost derivations.
Derivation 1 − X → X+X → a +X → a+ X*X → a+a*X → a+a*a
Parse tree 1 −
Derivation 2 − X → X*X → X+X*X → a+ X*X → a+a*X → a+a*a
Parse tree 2 −
Since there are two parse trees for a single string "a+a*a", the grammar G is ambiguous.
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