Consider the scattering of an electro-magnetic time-harmonic plane wave by an infinite cylinder having a mixed open crack in R2 as the cross section. We assume that the crack is made of two parts, and one of which is (possibly) coated on one side by a material with surface impedance A. The problem can be reformulated as a boundary integral system (BIS) by using potential theory. We obtain the existence and uniqueness of the weak ...