Definition:Complement


 * Complementary angles: two angles whose measures add up to the measure of a right angle.
 * Complement of Relation: for a relation $$\mathcal{R}$$, its complement is all those pairs which are not in $$\mathcal{R}$$.
 * Set Complement or Relative Complement: two related concepts: all the elements of a set which are not in a given subset.