At the poetry slam, three friends—Al, Betty and Chaz—sign up to perform six well-known poems,
designated here as Hop, Bop, Cop, Top, Sop and Mop. Each poem will be performed individually by one
poet, and each poem can only be performed once. To decide the order of the poems, the owner of the
coffee shop that organizes the poetry slam lays down the following rules:
• Hop must be performed before Top and before Mop.
• Cop must be performed after Bop and before Sop.
• Al can perform Hop, Bop and Sop.
• Betty can perform Cop, Top and Bop.
• Chaz can perform Hop, Mop and Top.
• Different poets must begin and end the slam, i.e. whatever poet performs the first poem
cannot perform the last one.