A supportive back rest for attachment to an original equipment back rest of a wheelchair to enhance the supportive characteristics of the wheelchair back rest. The computing device is to receive a challenge value and a first value from a host device, generate a second value based on at least the first value, and generate a response value based on the challenge value and the second value. The gaseous effluent and the condensed tar are fed to at least one knock-out drum, whereby the tar is separated from the gaseous effluent. The separating force is maintained at a minimum value so long as the releasable connector holds the struts in their first position. When the projection of a document onto the primary set of attributes is below a threshold, then a secondary set of attributes is used to supplement the primary lexicon so that the projection is above the threshold.