1987
4.3 Lattice structure filling Directly removing or adding material in the design space to search for the global optimal material topology solution is common to TO and generative design methods and , as stated above , there are many difficulties .
 engineering feature: Lattice structure; material: material; concept or principle: design space; material: material; concept or principle: solution; enabling technology: generative design; material: as
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: manufacturing standard, machanical property, manufacturing process, material, engineering feature, process parameter, machine or equipment, application, process characterization, enabling technology, biomedical, concept or principle 
Text: {0} 
Answer:
 engineering feature: Lattice structure; material: material; concept or principle: design space; material: material; concept or principle: solution; enabling technology: generative design; material: as