and c 4 hydrocarbon products e g the lines 34 and 36 respectively and separate and recover c 5 olefin hydrocarbon products e g the line 40 the c 5 olefin hydrocarbon products from the line 40 are introduced into an olefin cracking reactor 44 wherein the c 5 olefin hydrocarbon products are cracked to form a cracked olefin effluent shown as the line 46 comprising c 2 c 4 hydrocarbons including c 2 and c 3 olefins embodiments such as described above desirably provide or result in improved processing of a heavy hydrocarbon feedstock to produce an increased relative yield of light olefins and which processing is desirably more effective and or efficient than heretofore reasonably possible via conventional hydrocarbon cracking processing more specifically such embodiments through the targeted introduction or return of specified materials can significantly improve processing economics for example such processing can desirably minimize the amounts of materials requiring pressurization and or gas concentration product recovery processing in accordance with particular such embodiments a heavy hydrocarbon feedstock can be fluidized catalytically cracked to produce an effluent including a range of hydrocarbon products including c 4 c 7 olefins with at least a portion of such c 4 c 7 olefins subsequently being cracked to.