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The relation between number of links (l) and number of joints (j) in a kinematic chain is
l = (1/2).(j + 2)
l = (2/3).(j + 2)
l = (3/4).(j + 3)
l = j + 4
l = (1/2).(j + 2)
l = (2/3).(j + 2)
l = (3/4).(j + 3)
l = j + 4