Given an equivalence relation on a set, any one of the equivalence classes can be specified by giving one of the elements in it. The particular element a used can be called a representative of the class, and the class can be denoted by [a] or ā.
科学参考收录了60776条科技类词条，基本涵盖了常见科技类参考文献及英语词汇的翻译，是科学学习和研究的有利工具。