The routine returns true if l1 and l2 are tangent to each other; false if they are not; and FAIL if it is unable to determine if l1 and l2 are tangent to each other.

In case of FAIL, if the third optional argument is given, the condition that makes l1 and l2 tangent to each other is assigned to this argument. It will be either of the form  or of the form  where , ,  are maple expressions.

The command with(geometry,AreTangent) allows the use of the abbreviated form of this command.