1 Gravitational attraction is an equivalent expression of the force close to each other between and on the line of the two objects, coming from exchange of momentum between objects and micro-particles.

2 Sometimes it is difficult to find equivalent expression in one language.

3 Further, each expression has a method reduceDependencies(), which returns an equivalent expression in which specified dependencies are eliminated, while others are retained.

4 XSD data types can describe restrictions for which there is no equivalent expression in Java.

5 Due to the great differences between English and Chinese culture, the translator in translating culture-loaded words difficult to find the exact equivalent expression.