Fully articulated seats were offered as well. They have been fully articulated in the cases cited. The main rotor is fully articulated and has elastomeric bearings in the rotor head. The idea was first articulated by Independents within the Puritan movement. The spines are articulated and comparatively flexible, but relatively blunt. Coptologists believe that Coptic was articulated as a voiced bilabial fricative . The skeleton is largely articulated and not compressed. The principle was first articulated explicitly in 1981 by Saltzer, Reed, and Clark. Various designs for articulated locomotives were developed to overcome this problem. Inevitably any such locomotive will be articulated. This view has been articulated by advocates of deep history. AGCO developed the Agcostar line of articulated tractors. It represents a complete and mostly articulated skeleton with skull. Through his writings, Simons articulated and formalized the teachings of earlier Swiss founders. The system was lightweight, with stations designed for trains of only a single articulated vehicle.