use `patch` here?

[affeldt-aist]

analysis/theories/lebesgue_integral.v

Line 3420 in c518e2a

\int[mu]_(x in E `&` D) f x = \int[mu]_(x in E) (f x * (\1_D x)%:E).

i.e., f \_ D instead of f \* \1_ D ?