English
Under reflection, the bottom coefficient with i and j equals the top coefficient with i and j swapped accordingly.
Русский
При отражении снизу коэффициент с i и j соответствует верхнему коэффициенту с i и j переставленными.
LaTeX
$$$$ P.chainBotCoeff(i, P.reflectionPerm(j,j)) = P.chainTopCoeff(i, j) $$$$
Lean4
@[simp]
theorem chainBotCoeff_reflectionPerm_right : P.chainBotCoeff i (P.reflectionPerm j j) = P.chainTopCoeff i j :=
by
letI := P.indexNeg
have (z : ℤ) :
z ∈ Icc (-P.chainTopCoeff i j : ℤ) (P.chainBotCoeff i j) ↔
z ∈ Icc (-P.chainBotCoeff i (-j) : ℤ) (P.chainTopCoeff i (-j)) :=
by rw [P.chainCoeff_reflectionPerm_right_aux]
refine le_antisymm ?_ ?_
· simpa using this (-P.chainBotCoeff i (-j))
· simpa using this (-P.chainTopCoeff i j)