1960
It is not difficult to image that embedding AM constraints into an evolutionary TO process would be more difficult than that of density or level set based methods since the process uses discrete optimization .
 concept or principle: image; manufacturing process: AM; concept or principle: process; material: be; machanical property: density; application: set; concept or principle: process; enabling technology: discrete optimization
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:
 concept or principle: image; manufacturing process: AM; concept or principle: process; material: be; machanical property: density; application: set; concept or principle: process; enabling technology: discrete optimization