Published online by Cambridge University Press: 08 September 2017
The following will be shown: Let I be a σ-ideal on a Polish space X so that the associated forcing of I+${\bf{\Delta }}_1^1$ sets ordered by ⊆ is a proper forcing. Let E be a
${\bf{\Sigma }}_1^1$ or a
${\bf{\Pi }}_1^1$ equivalence relation on X with all equivalence classes
${\bf{\Delta }}_1^1$. If for all
$z \in {H_{{{\left( {{2^{{\aleph _0}}}} \right)}^ + }}}$, z♯ exists, then there exists an I+
${\bf{\Delta }}_1^1$ set C ⊆ X such that E ↾ C is a
${\bf{\Delta }}_1^1$ equivalence relation.