Figure 4: Phase closure technique for phasing low-redundancy interferometric arrays on a reference star. For a point source, the Fourier transform (A) of the recombined image is the autocorrelation of the exit pupil (B). For a resolved star, the pattern (A) is approximately multiplied by the star's complex visibility (C). To activate the adaptive corrector, the N atmospheric-instrumental phases are derived from the calculated phases in the N(N-1)^/2 cones. The inversion requires that the N(N-1)^/2 object phases be oversampled. The object phase being smooth at the scale of the speckles in (C), some of the speckles must contain several cones. The condition may be satisfied with N cones in the central peak, as achieved if the object is unresolved by the smallest baseline.