type ℕ = Int;

fn Σ(a: ℕ, b: ℕ) -> ℕ {
    return a + b;
} 

if Σ(4, 5) != 9 {
    panic("This should not happen");
}

binary op "⊕" (5);

op (a: ℕ) ⊕ (b: ℕ) -> ℕ {
    return a * 2 + b * 2;
}

if 4 ⊕ 5 != 18 {
    panic("This should not happen");
}