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 akafanana 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 nzvimbo iri pakati pemirazi yakakamurwa nekukurumidza kwechiedza. Asi kana mucherechedzi ari pawachi B, anoona kuti wachi inoitika mukati mechiratidzo chewachi, B anoteedzera chiratidzo, 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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