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   We propose an ASCA study of the surroundings of RX J174537.0+3951,
   which was recently identified as a BL Lac from the ROSAT--5 GHz Green
   Bank correlations. The BL Lac lives in a truly exceptional optical
   environment. The object is associated with a galaxy which is the end of
   a linear chain of compact objects. South of the BL Lac is a large arc -
   the only arc known to be associated with an AGN up to now. The arc
   indicates gravitaional lensing and thus the BL Lac might reside in a
   currently unknown cluster of galaxies. The ASCA study aims at
   investigating the X-ray emission of the BL Lac and its surroundings, in
   order to determine the origin of the X-ray emission by means of its X-
   ray spectrum. The ASCA observation complements a detailed spatial
   analysis with ROSAT HRI.
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