(F,G) = makeS2 R
A ring $S$ satisfies Serre's S2 condition if every codimension 1 ideal contains a nonzerodivisor and every principal ideal generated by a nonzerodivisor is equidimensional of codimension one. If $R$ is an affine reduced ring, then there is a unique smallest extension $R\subset S\subset {\rm frac}(R)$ satisfying S2, and $S$ is finite as an $R$-module.
Uses the method of Vasconcelos, "Computational Methods..." p. 161, taking the idealizer of a canonical ideal.
There are other methods to compute $S$, not currently implemented in this package. See for example the function (S2,Module) in the package "CompleteIntersectionResolutions".
We compute the S2-ification of the rational quartic curve in $P^3$
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Assumes that first element of canonicalIdeal R is a nonzerodivisor; else returns error. The return value of this function is likely to change in the future
The object makeS2 is a method function with options.