English
The core of a composed relation equals the core of the outer relation applied to the core of the inner: core(R ○ S) u = core(R)(core(S)u).
Русский
Ядро композиции отношений удовлетворяет: core(R ○ S) u = core(R)(core(S) u).
LaTeX
$$R.\mathrm{core}(R \circ S)(u) = R.\mathrm{core}(S.\mathrm{core}(u))$$
Lean4
theorem core_comp : core (R ○ S) u = core R (core S u) := by aesop