A function, f, on a metric space, X, which decreases the distance, d, between any two points in X by at least some given factor, i.e. there exists a<1, d(f(x), f(y)) ≤ a×d(x, y) for all x, y in X.
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。