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The second class of topology optimization methods , represented by the level-set algorithm , focus on tracking phase boundaries .
 engineering feature: topology optimization; concept or principle: algorithm; concept or principle: phase boundaries
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: topology optimization; concept or principle: algorithm; concept or principle: phase boundaries