▁ ▁revers al ▁[ R ] ▁( A ▁+ ▁B ▁with ▁closure ) ▁ ▁reg ist ral ▁return ▁[ aba ] ▁( ex act ▁or ▁nearly ▁exact ▁return ▁to ▁same ▁pitch ) ▁ ▁dy ad ▁( two ▁imp lic ative ▁items , ▁as ▁in ▁ 1 ▁and ▁ 2 , ▁without ▁a ▁real ization ) ▁ ▁mon ad ▁( one ▁element ▁which ▁does ▁not ▁yield ▁an ▁imp lication ) ▁ ▁Central ▁to ▁the ▁discussion ▁is ▁the ▁notion ▁of ▁reg ist ral ▁direction ▁( direction ▁of ▁motion ) ▁and ▁size ▁of ▁intervals ▁between ▁pairs ▁of ▁pitch es . ▁ ▁[ P ] ▁( process ) ▁refers ▁to ▁motion ▁in ▁the ▁same ▁reg ist ral ▁direction ▁combined ▁with ▁similar ▁inter v all ic ▁motion ▁( two ▁small ▁intervals ▁or ▁two ▁large ▁intervals ). ▁[ D ] ▁refers ▁to ▁identical ▁inter v all ic ▁motion ▁with ▁later al ▁reg ist ral ▁direction . ▁[ R ] ▁refers ▁to ▁changing ▁inter v all ic ▁motion ▁( large ▁to ▁smaller ) ▁with ▁different ▁reg ist ral ▁directions . ▁ ▁P , ▁D , ▁and ▁R ▁only ▁account ▁for ▁cases ▁where ▁reg ist ral ▁direction ▁and ▁interval ic ▁motion ▁are ▁working ▁in ▁un ison ▁to ▁satisfy ▁the ▁imp lications . ▁When ▁one ▁of ▁these ▁two ▁factors ▁is ▁denied , ▁there ▁are ▁more ▁possibilities , ▁the ▁five ▁arch et yp al ▁derivatives : ▁▁ ▁inter v all ic ▁process ▁[ IP ]: ▁small ▁interval ▁to ▁similar ▁small ▁interval , ▁different ▁reg ist ral ▁directions ▁ ▁reg ist ral ▁process ▁[