Ina noho ngā tau whakarea ki ngā tau tōpū, ngā tau haumaru, tētahi āpure paetata rānei, he hātepe hei whakamātau i te korekoretanga, hei tatau hoki i te whakarea ki ngā taumaha whakakoretia (tirohia te Factorization o ngā taumaha).