As noted above, it is usual to express the condition <math>(X, Y) \in \mathfrak{K}</math> by writing <math>X :> Y \, \text{in} \, \mathfrak{G}.</math>
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This relation is indicated by saying that W "immediately derives" W',
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that W' is "immediately derived" from W in !G!, and also by writing:
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This relation is indicated by saying that <math>W\!</math> ''immediately derives'' <math>W',\!</math> by saying that <math>W'\!</math> is ''immediately derived'' from <math>W\!</math> in <math>\mathfrak{G},</math> and also by writing:
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W ::> W'.
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{| align="center" cellpadding="8" width="90%"
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| <math>W ::> W'.\!</math>
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|}
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<pre>
A "derivation" in !G! is a finite sequence (W_1, ..., W_k)
A "derivation" in !G! is a finite sequence (W_1, ..., W_k)
of sentential forms over !G! such that each adjacent pair
of sentential forms over !G! such that each adjacent pair