Atomic Properties of the Hawaiian Earring Group for HNN Extensions

In 2011, while investigating fundamental groups of wild spaces, K.Eda [7 Eda , K. ( 2011 ). Atomic property of the fundamental groups of the Hawaiian earring and wild locally path-connected spaces . Jour. Math. Soc. Japan 63 ( 3 ): 769 – 787 .[Crossref], [Web of Science ®] , [Google Scholar]] showed that the fundamental group of the Hawaiian earring (the Hawaiian earring group, in short) has the property that for any homomorphism h from it to a free product A*B, there exists a natural number N such that is contained in a conjugate subgroup to A or B. In the present article, we prove a corresponding property for certain HNN extensions and amalgamated free products. This allows us to show that some one-relator groups, including Baumslag–Solitar groups, are n-slender.