 In the literature, however, one may also find a less-standard reading of negated implications (and consequently also a corresponding non-standard understanding of negated co-implications). This unusual reading of negated implications is usually tracked back to Aristotle and Boethius, and is referred to as the connexive version of (negated) implications (cf. Wansing 2005, McCall 2012 and the  connexive logic  entry). Equivalences characteristic of connexive implication and co-implication are: