param k = 2        a number you can drag (a weight)
const dt = 1 / 60  a number that stays put
fn f(x, y) -> (a, b) { ... }   one function: inputs -> outputs
let d = x * x + y   name a value
return (d, -d)       one value per output

x + y   x - y   x * y   -x   (...)
x / 2         divide by a number (not by a variable)
x < y  x > y  1 if true, else 0
if x < 0 { -x } else { x }    else if chains too
abs(x)        and nothing else: no loops, no sin

The fn's shape picks the display: (x) a curve, (x, y) a picture
(1 output grey, 3 colour), (x, y, t) a moving one, (a, b) -> (a, b)
a step, repeated. Copy link shares your code.