Problem with almost everywhere equality
  A topological space $Y$ is said to have (AEEP) if the following condition is fulfilled. Whenever $(X,\mathfrak{M})$ is a measurable space and $f, g: X \to Y$ are two measurable functions, then the set $\Delta(f,g) = \{x \in X:\ f(x) = g(x)\}$ is a member of $\mathfrak{M}$. It is shown that a metrizable space $Y$ has (AEEP) iff the cardinality of $Y$ is no greater than $2^{\aleph_0}$. 
Piotr Niemiec
math.GN