in geometry, the word congruence is often preferred. numbers are equal, geometrical objects are congruent. two shapes are congruent if one can be moved or rotated so that it fits exactly where the other one is. if shrinking or enlarging one of the two objects is needed, then they are not congruent. they are called "similar" instead. the congruence relation is often represented by the symbol formula_3, while the similarity relation is represented by the symbol formula_1.