Let ( X , M ) {\displaystyle (X,M)} and ( Y , N ) {\displaystyle (Y,N)} be measure spaces. A map f : X → Y {\displaystyle f:X\to Y} is ( M , N ) {\displaystyle (M,N)} -measurable if f − 1 ( E ) ∈ M {\displaystyle f^{-1}(E)\in M} for all E ∈ N . {\displaystyle E\in N.}
