A non-transitory machine readable storage medium encoded with instructions executable by a processor and comprising instructions to: receive object data corresponding to a three-dimensional object to be generated in a layer-wise manner; for each of a plurality of slices of the object, define print data to control a respective layer forming operation in which print agent is ejected on a layer of build material in a pattern corresponding to selective fusing of the build material, wherein the print data and the respective pattern is defined for each slice according to a print definition procedure characterized in that said storage medium further comprises instructions to select the print definition procedure from a plurality of print definition procedures based on a user input; wherein each of the print definition procedures is to define a pattern for forming a respective layer of the object including a slice boundary and a fusing reduction region to inhibit excess fusing outside the slice boundary ; and wherein at least one of: a location instruction to define a location of the fusing reduction region relative the respective slice boundary ; a scheduling instruction to schedule the ejection of print agent during a respective layer forming operation to define the fusing reduction region ; and a concentration instruction to define a concentration of print agent for defining the fusing reduction region ; varies between the print definition procedures. receive object data corresponding to a three-dimensional object to be generated in a layer-wise manner; for each of a plurality of slices of the object, define print data to control a respective layer forming operation in which print agent is ejected on a layer of build material in a pattern corresponding to selective fusing of the build material, wherein the print data and the respective pattern is defined for each slice according to a print definition procedure characterized in that said storage medium further comprises instructions to select the print definition procedure from a plurality of print definition procedures based on a user input; wherein each of the print definition procedures is to define a pattern for forming a respective layer of the object including a slice boundary and a fusing reduction region to inhibit excess fusing outside the slice boundary ; and wherein at least one of: a location instruction to define a location of the fusing reduction region relative the respective slice boundary ; a scheduling instruction to schedule the ejection of print agent during a respective layer forming operation to define the fusing reduction region ; and a concentration instruction to define a concentration of print agent for defining the fusing reduction region ; varies between the print definition procedures. a location instruction to define a location of the fusing reduction region relative the respective slice boundary ; a scheduling instruction to schedule the ejection of print agent during a respective layer forming operation to define the fusing reduction region ; and a concentration instruction to define a concentration of print agent for defining the fusing reduction region ; varies between the print definition procedures. <EOS>