Relation Command
 Relation( <List> )

Shows a message box that gives you information about the relation between two or more (up to 4) objects.
 Relation( <Object>, <Object> )

Shows a message box that gives you information about the relation between two objects.
This command allows you to find out whether

two lines are perpendicular

two lines are parallel

two (or more) objects are equal

a point lies on a line or conic

a line is tangent or a passing line to a conic

three points are collinear

three lines are concurrent (or parallel)

four points are concyclic (or collinear).
Some of these checks can also be performed symbolically. If GeoGebra supports symbolic check for a certain property, the "More" button appears. By clicking it, GeoGebra may provide more information whether the property is true in general (eventually under certain conditions).
See also Relation tool. 