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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def com_google_fonts_check_negative_advance_width(ttFont):
 """ Check that advance widths cannot be inferred as negative. """

  failed = False
  for glyphName in ttFont["glyf"].glyphs:
    coords = ttFont["glyf"][glyphName].coordinates
    rightX = coords[-3][0]
    leftX = coords[-4][0]
    advwidth = rightX - leftX
    if advwidth < 0:
      failed = True
      yield FAIL, ("glyph '{}' has bad coordinates on the glyf table,"
                   " which may lead to the advance width to be"
                   " interpreted as a negative"
                   " value ({}).").format(glyphName,
                                          advwidth)
  if not failed:
    yield PASS, "The x-coordinates of all glyphs look good."