Condition in sequence diagram

UML
1

hello.
i want to show conditions on this object but i ma not able to show it…

please any once can make its sequence diagram.

Bool:isMBRIntersect(Archive& other)
{
moveToMBR();
other.moveToMBR();

MBR m1, m2;
m1 = getMBR();
m2 = other.getMBR();

if (m1.high_[0] < m2.low_[0]) return FALSE;
if (m1.high_[1] < m2.low_[1]) return FALSE;
if (m1.low_[0] > m2.high_[0]) return FALSE;
if (m1.low_[1] > m2.high_[1]) return FALSE;

return TRUE;

}

i am using alt combined frame but i want to apply conditions but i did not get success.
any on can make its sequence diagram