Beschreibung:
<jats:title>Abstract</jats:title><jats:p>The question of whether ribbon-disc complements—or, equivalently, standard 2-complexes over labelled oriented trees—are aspherical is of great importance for Whitehead’s asphericity conjecture and, if solved affirmatively, would imply a combinatorial proof of the asphericity of knot complements. We present here two classes of diagrammatically reducible labelled oriented trees.</jats:p><jats:p>AMS 2000 <jats:italic>Mathematics subject classification:</jats:italic> Primary 57M20; 20F06; 20F05; 20F32</jats:p>