Spindle configurations of skew lines
  We prove a conjecture of Crapo and Penne which characterizes isotopy classes of skew configurations with spindle-structure. We use this result in order to define an invariant, spindle-genus, for spindle-configurations.   We also slightly simplify the exposition of some known invariants for configurations of skew lines and use them to define a natural partition of the lines in a skew configuration.   Finally, we describe an algorithm which constructs a spindle in a given switching class, or proves non-existence of such a spindle. 
Roland Bacher (Institut Fourier), David Garber (Institut Fourier)