  On 23 July 2016 after 05:00\,UTC, the first 48-antenna stage of the Siberian
Radioheliograph detected two flares of M7.6 and M5.5 GOES importance that
occurred within half an hour in the same active region. Their multi-instrument
analysis reveals the following. The microwave spectra were flattened at low
frequencies and the spectrum of the stronger burst had a lower turnover
frequency. Each flare was eruptive, emitted hard X-rays and gamma-rays
exceeding 800\,keV, and had a rare three-ribbon configuration. An extended hard
X-ray source associated with a longest middle ribbon was observed in the second
flare. The unusual properties of the microwave spectra are accounted for by a
distributed multi-loop system in an asymmetric magnetic configuration that our
modeling confirms. Microwave images did not to resolve compact configurations
in these flares that may also be revealed incompletely in hard X-ray images
because of their limited dynamic range. Being apparently simple and compact,
non-thermal sources corresponded to the structures observed in the extreme
ultraviolet. In the scenario proposed for two successive three-ribbon eruptive
flares in a configuration with a coronal-null region, the first eruption causes
a flare and facilitates the second eruption that also results in a flare.
