For any lumped network, for any cut sets and at any instant of time the algebraic sum of all branch currents traversing the cut-set branches is always:

Fundamental cut-set: Fundamental cut set is a cut through a given graph which divides into two parts but in its path of cutting it should encounter only one twig.

The path of cut set forms a voltage line, it is called a cut set voltage. The orientation of this cut–set voltage is given by the twig governing it.

The number of cut set for any graph = n – 1 = number of twigs.

A fundamental cut-set of a graph with respect to a tree is a cut-set formed by one and only one twig and a set of links.

Cut set of a connected graph is a set of branches, which cuts the given graph into two separate parts such that the removal of all branches of the set causes the remaining graph to have separate parts.

From KCL, for any lumped network, for any of its cut sets and at any time, the algebraic sum of all branch currents traversing the cut-set branches is always zero.

, for any lumped network, for any of its loops and at any time, the algebraic sum of all branch voltages around the loop is always zero.