6 " ▁For ▁a ▁P ian ist , ▁it ▁uses ▁similar ▁notation ▁and ▁compos itional ▁techniques , ▁but ▁is ▁much ▁easier ▁to ▁play . ▁The ▁rh yth mic ▁structure ▁is ▁also ▁identical ▁to ▁ 3 4 ' 4 6 . 7 7 6 ". ▁ ▁Two ▁prepared ▁pian os ▁ ▁A ▁Book ▁of ▁Music ▁Com posed ▁in ▁ 1 9 4 4 . ▁Like ▁the ▁later ▁work , ▁Three ▁D ances ▁( 1 9 4 5 ), ▁A ▁Book ▁of ▁Music ▁was ▁commission ed ▁by ▁pian ists ▁Robert ▁F iz dale ▁and ▁Arthur ▁Gold . ▁It ▁was ▁C age ' s ▁first ▁work ▁written ▁on ▁request ▁from ▁professional ▁perform ers . ▁There ▁are ▁two ▁movements , ▁each ▁divided ▁into ▁several ▁smaller ▁sections ▁( four ▁in ▁the ▁first ▁movement , ▁three ▁in ▁the ▁second ). ▁The ▁music ▁makes ▁much ▁use ▁of ▁scales ▁and ▁ar p eg g ios ▁and ▁features ▁much ▁virt u os ic ▁writing . ▁According ▁to ▁C age , ▁this ▁was ▁inspired ▁by ▁his ▁ideas ▁on ▁Moz art ' s ▁music , ▁which ▁" str ict ly ▁ad her es ▁to ▁three ▁different ▁kinds ▁of ▁scales : ▁the ▁chrom atic , ▁the ▁di at onic , ▁and ▁that ▁consisting ▁of ▁the ▁larger ▁steps ▁of ▁third s ▁and ▁fourth s ". ▁The ▁technique ▁of ▁rh yth mic ▁proport ions ▁is ▁used ▁in ▁a ▁new ▁way : ▁the ▁proportion ▁for ▁each ▁piece ▁is ▁defined ▁for ▁a ▁particular ▁tempo . ▁A ▁change ▁in ▁the ▁tempo ▁causes ▁a ▁change ▁in ▁the ▁proportion . ▁ ▁Three