import data.num

section
parameter {A : Type}
definition f (a b : A) := a
infixl `◀`:65 := f
parameters a b : A
check a ◀ b
end

inductive list (T : Type) : Type :=
nil {} : list T,
cons   : T → list T → list T

namespace list
section
variable {T : Type}
notation `[` l:(foldr `,` (h t, cons h t) nil) `]` := l
check [10, 20, 30]
end
end list

open list
check [10, 20, 40]
check 10 ◀ 20