Affirming a disjunct

The formal fallacy of affirming a disjunct also known as the fallacy of the alternative disjunct or a false exclusionary disjunct occurs when a deductive argument takes the following logical form:^[1]

A or B

A

Therefore, not B

Or in logical operators:

${\displaystyle p\vee q}$

${\displaystyle p}$

${\displaystyle {}\vdash {}}$ ¬ ${\displaystyle q}$

Where ${\displaystyle {}\vdash {}}$ denotes a logical assertion.