@Article{	  KufleitnerLauser12dmtcs,
  author	= "Manfred Kufleitner and Alexander Lauser",
  title		= "The Join of the Varieties of {R}-trivial and {L}-trivial
		  Monoids via Combinatorics on Words",
  journal	= "Discrete Mathematics {\&} Theoretical Computer Science",
  volume	= "14",
  number	= "1",
  year		= "2012",
  pages		= "141--146",
  abstract	= "The join of two varieties is the smallest variety
		  containing both. In finite semigroup theory, the varieties
		  of $\mathcal{R}$-trivial and $\mathcal{L}$-trivial monoids
		  are two of the most prominent classes of finite monoids.
		  Their join is known to be decidable due to a result of
		  Almeida and Azevedo. In this paper, we give a new proof for
		  Almeida and Azevedo's effective characterization of the
		  join of $\mathcal{R}$-trivial and $\mathcal{L}$-trivial
		  monoids. This characterization is a single identity of
		  $\omega$-terms using three variables."
}