HR DL U ▁was ▁derived ▁from ▁E TA OIN ▁S HR DL U , ▁the ▁arrangement ▁of ▁the ▁letter ▁keys ▁on ▁a ▁Lin ot ype ▁machine , ▁arranged ▁in ▁desc ending ▁order ▁of ▁usage ▁frequency ▁in ▁English . ▁ ▁Function ality ▁S HR DL U ▁was ▁primarily ▁a ▁language ▁parser ▁that ▁allowed ▁user ▁interaction ▁using ▁English ▁terms . ▁The ▁user ▁instruct ed ▁S HR DL U ▁to ▁move ▁various ▁objects ▁around ▁in ▁the ▁" block s ▁world " ▁containing ▁various ▁basic ▁objects : ▁blocks , ▁con es , ▁balls , ▁etc . ▁What ▁made ▁S HR DL U ▁unique ▁was ▁the ▁combination ▁of ▁four ▁simple ▁ideas ▁that ▁added ▁up ▁to ▁make ▁the ▁simulation ▁of ▁" under standing " ▁far ▁more ▁convin cing . ▁ ▁One ▁was ▁that ▁S HR DL U ' s ▁world ▁was ▁so ▁simple ▁that ▁the ▁entire ▁set ▁of ▁objects ▁and ▁locations ▁could ▁be ▁described ▁by ▁including ▁as ▁few ▁as ▁perhaps ▁ 5 0 ▁words : ▁ ▁n oun s ▁like ▁" block " ▁and ▁" con e ", ▁ver bs ▁like ▁" place ▁on " ▁and ▁" move ▁to ", ▁and ▁ad ject ives ▁like ▁" big " ▁and ▁" blue ". ▁The ▁possible ▁combinations ▁of ▁these ▁basic ▁language ▁building ▁blocks ▁were ▁quite ▁simple , ▁and ▁the ▁program ▁was ▁fairly ▁ade pt ▁at ▁fig uring ▁out ▁what ▁the ▁user ▁meant . ▁ ▁S HR DL U ▁also ▁included ▁a ▁basic ▁memory ▁to ▁supply ▁context . ▁One ▁could ▁ask ▁S HR DL U ▁to ▁" put ▁the ▁green ▁cone ▁on