•Given a structure A and formula f(R, x), define the following operator Ff : P(A) ! P(A):
Ff(X) = { a | A ² f(X/R, a) }
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•The meaning of [lfpR, x f(R, x)][t] is lfp(Ff)
•The meaning of [ifpR, x f(R, x)][t] is ifp(Ff)
•The meaning of [pfpR, x f(R, x)][t] is pfp(Ff)
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