13 or if desired such link arms could have an angular configuration similar to a bell crank it is apparent that the first hinge member 23 is slidably connected to the second hinge member 24 by the pin 28 located within the control slot 47 and that one end of the link 48 is pivotally connected to the first hinge member by the pin 50 while the other end of such link is pivotally connected to the second hinge member by the pin 51 relative movement between the arcuate control slot 47 and the associated guide pin 28 causes the link 48 to swing about the pins 50 and 51 and confines both the leading and trailing edges of the door 21 to rationally chosen desired paths the shape of the arcuate control slot 47 ordinarily is determined by plotting a selected path for the trailing edge of the door and relating the necessary positions of the pins 50 and 51 and the link 48 to a set of coordinate points along the central rib 43 therefore relative movement between the slot 47 and the guide pin 28 transmits the information contained in the bearing surfaces of the control slot to the pivot pins and link thus necessarily recreating the selected paths of movement of the leading and trailing edges of the door in order for the leading and trailing edges of the door to follow the same controlled path each time the door is moved the guide pin 28 and the pivot pin 50 are spaced apart a fixed predetermined distance the pivot pins 50 and 51 are spaced apart a fixed predetermined distance and the distance between.