One or more barrier members is coupled at a fixed post to a pivot pin or axis oriented parallel to {HEAD ~ the extension direction} of {TAIL ~ the parallelogram linkage}, and thus operable to guide the barrier gate to a blocking position spanning the doorway or to rotate back around the pivot pin to a retracted position at the fixed posts or behind the fixed posts relative to the doorway opening 
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One or more barrier members is coupled at a fixed post to a pivot pin or axis oriented parallel to { HEAD ~ the extension direction } of { TAIL ~ the parallelogram linkage } , and thus operable to guide the barrier gate to a blocking position spanning the doorway or to rotate back around the pivot pin to a retracted position at the fixed posts or behind the fixed posts relative to the doorway opening
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