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==== As a ring of formal power series ====
The easiest (though somewhat heavy) construction starts with the ring of [[Formal_power_series#Power_series_in_several_variables|formal power series]] ''R''[[''X''<sub>1</sub>,''X''<sub>2</sub>,…]] over ''R'' in infinitely many indeterminates; one defines Λ<sub>''R''</sub> as its subring consisting of power series ''S'' that satisfy
#''S'' is invariant under any permutation of the indeterminates, and
#the degrees of the monomials occurring in ''S'' are bounded.
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