Lewis naTolman (1909) vakatsanangura kuwirirana kwekupararira kwenguva vachishandisa wachi mbiri dzechiedza A naB, vachifamba nekumhanya kwakati kune mumwe nemumwe. Maawa acho ane magirazi maviri epasi akaenzana kune mumwe nemumwe uye kune mutsara wekufamba. Pakati pemirazi chiratidzo chechiedza chiri kudzoka, uye kune mucherechedzi akazorora mune imwecheteyo inoreva seA, nguva yeawa yeA ndiyo kureba pakati pemirazi yakakamurwa nekumhanya kwechiedza. Asi kana mucherechedzi ari pawachi B, anoona kuti wachi inoitika mukati mechiratidzo chakabuda, B inoteedzera chiratidzo chakabuda, B. Uye Lewis naTolman (1909) vakatsanangura kuwirirana kwekupararira kwenguva vachishandisa wachi mbiri dzechiedza A naB, vachifamba nekumhanya kwakati kune mumwe nemumwe.
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