An agricultural implement includes first and second outer harrows positioned adjacent front and left sides and front and right sides of a frame, respectively, at generally opposite diagonal directions. Each contact has a retaining portion retained on the first or second rear housings, a contact portion forwardly extending beyond a front end of the first and second rear housings to affix to the tongue, and a tail portion extending out of the first and second rear housings. This invention provides a method of determining whether a compound enhances formation of a complex between a p66 and p51 subunit polypeptides of HIV-1 reverse transcriptase. A torque-master-slave controller ensures a compensation of the torques between the drive units. Moreover, an exemplary embodiment of a roofing shingle employing a nonwoven fiber material as described herein is as disclosed. The leg supports are pivotally engaged through two first hinge elements.