{1, 2, 3} : set ℕ
{1} : set ℕ
∅ : set ℕ
def s1 : set ℕ :=
{1, 2 + 3, 3, 4}
def s2 : set char :=
{#"a", #"b", #"c"}
def s3 : set string :=
{"hello", "world"}
{a ∈ s1 | a > 1} : set ℕ
{a ∈ s1 | a > 1} : set ℕ
{a in s1 | a > 2} : set nat
{a, a} : set nat
{a, 1, a} : set nat
{a} : set nat
{a // a > 0} : Type