◆ LIT — verified / checkable
Time-difference-of-arrival: a receiver pair with arrival-time difference Δt constrains the emitter to a hyperbola — the locus of points whose distances to the two receivers differ by exactly c·Δt (the two receivers are its foci). Each independent pair gives one hyperbola; two pairs (three receivers) intersect at the source, more tighten it. This is real multilateration — how a network locates a phone, a gunshot, or a lightning stroke it never announced. The drawn hyperbolae pass through the true emitter.
▲ AMBER — the figure
A 2-D, noise-free toy with instantaneous, perfectly-synchronised receivers. Real systems fight clock sync between stations, multipath, and geometry (poor receiver layout blows up the error). The hyperbola-from-a-time-difference is the exact, real locus.
a point is fixed from THREE — and the point they fix is Top, at the centre.