English
If a and b both possess substitutions, then composing substAlgHom with hb and ha yields a substitution of the composed substitution ha.comp hb.
Русский
Если подстановки a и b существуют, то композиция substAlgHom hb и ha образует подстановку от сложной подстановки ha.comp hb.
LaTeX
$$$\\text{HasSubst}(a) \\to \\text{HasSubst}(b) \\to \\text{HasSubst} (\\text{substAlgHom hb} a)$$$
Lean4
theorem comp {a : PowerSeries S} (ha : HasSubst a) {b : MvPowerSeries υ T} (hb : HasSubst b) :
HasSubst (substAlgHom hb a) :=
MvPowerSeries.IsNilpotent_subst hb.const ha