Question about defining grammars -

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i studying grammars , bit confused how design grammars 1 value dependent on another.

for example, want define grammar produces following 3 sentences:

i + = ii : base case

iiii + ii = iiiiii (thats 4 i's + 2 i's equals 6 i's)

iii + = iiii (3 i's + 1 equals 4 i's)

how go this? part confuses me if first 'value' iiii second can 'ii' , not 'i' or 'iii'.

thanks in advance!

grammars trivial if language finite:

s → "i + = ii" s → "iiii + ii = iiiiii" s → "iii + = iiii"

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