Mac Lane's planarity criterion

Mac Lane's planarity criterion

In graph theory, Mac Lane's planarity criterion is a characterisation of planar graphs in terms of their cycle spaces. It states that a finite graph "G" is planar if and only if the cycle space "C"("G"), which in topologists' terms is the space of 1-cycles with mod 2 coefficients of "G" as simplicial complex, has a 2-basis, i.e. a vector space basis over the field with two elements, such that a given edge appears in at most two basis vectors. The "only if" direction is intuitively clear. This result is due to Saunders Mac Lane (1937).

References

* S. Mac Lane, "A combinatorial condition for planar graphs", Fund. Math. 28 (1937), 22–32.


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