The item generated by the production A → ɛ is : 

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UGC NET Computer Science (Paper 2) 11 March 2023 Official Paper
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  1. A → .
  2. A → ε.
  3. A → .ε
  4. A → ε

Answer (Detailed Solution Below)

Option 1 : A → .
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UGC NET Paper 1: Held on 21st August 2024 Shift 1
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Detailed Solution

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The correct answer is A → .

 Key Points

  • In the context of LR parsing in the field of computer science, an 'item' of a grammar rule represents a partially recognized rule. The dot in the item is used to indicate how much of a rule has been seen at a particular point in the parse process.
  • For example, if we have a rule such as A -> BCD, when parsing begins, no part of the right side has been recognized, so the initial item is A -> .BCD. As parsing proceeds and B, C, and D are recognized, the dot moves rightward: A -> B.CD,  A -> BC.D, and A -> BCD. respectively.
  • Now, let's consider your rule A -> ε, which means that A can produce an empty string (epsilon). In the context of recognizing this rule, initially we've seen none of it, hence the item is A -> .. After recognizing the ε (meaning, recognizing that there's nothing to recognize), the item would be A -> ε..
  • So, where we haven't parsed any symbols yet, the correct representation would be A -> .. The 'ε' isn't generally shown in the item because the dot alone indicates that no part of the right hand side has been seen, which is appropriate for a production that generates the empty string.
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