@Article{PMV05,
    Author       = "Padmanabhan, R. and McCune, B. and Veroff, R.",
    Year         = "2005",
    Title        = "{Levi's Commutator Theorems for Cancellative Semigroups}",
    Journal      = "Semigroup Forum",
    Volume       = "71",
    Pages        = "152-157",
    Comment      = "TPTPRef"
}