  In the first part, we introduce a notion a degree of edge-colorings of
bicubic plane graphs and proves some local formula of the graded number of
colorings. In the second part, we give a new proof of a result of Fisk saying
that any two edge-3-colorings of a planar bicubic graph are Kempe equivalent.
Additionaly we show that the degree of colorings behaves well with respect to
Kempe equivalence.
