Sentence:  We first define a <WSD>function</WSD> b ( t ) as follows : given the set of squares such that each has three corners on C and vertex at t , b ( t ) is the corresponding set of positive parametric differences between t and the backward corner points . 
Meaning of the word marked with <WSD> tags:  (mathematics) a mathematical relation such that each element of a given set (the domain of the function) is associated with an element of another set (the range of the function)