SUPERPOSITION

Two travelers passing forever — their sum stands still.

y₁+y₂ = 2A·cos(πΔf·t)·cos(2πf̄t) — the throb piano tuners count.

Darkness made of light — d·sinθ = mλ, and only ⌊d/λ⌋ fringes exist.

One open slit still forbids directions — a·sinθ = mλ dark, the central hub twice a side band, every d/a-th double-slit order missing.

Soap-film colors: 2nt = (m−½)λ — and a hidden half-flip makes a vanishing film go black, not bright.

d·sinθ = mλ run backwards — measure an angle, recover the light, residual zero.

One exact stationary wave, matched twice: density may decay inside the barrier while probability current crosses and R + T stays one.