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A graph is k-choosable if it can be colored whenever every vertex has a list of at least k available colors. A theorem by Grötzsch  asserts that every triangle-free planar graph is 3-colorable. On the other hand Voigt  found such a graph which is not 3-choosable. We prove that if a triangle-free planar graph is not 3-choosable, then it contains a 4-cycle that intersects another 4-or 5-cycle in exactly one edge. This strengthens the Thomassen's result  that every planar graph of girthdoi:10.1137/080743020 fatcat:qq6666y2b5bk5f5kw3reox6rbu