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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 check_crs(crs):
 """ Checks if the crs represents a valid grid, projection or ESPG string. (Code copied from https://github.com/fmaussion/salem) Examples -------- '+units=m +init=epsg:26915 ' True Returns ------- A valid crs if possible, otherwise None """

    import pyproj
    if isinstance(crs, pyproj.Proj):
        out = crs
    elif isinstance(crs, dict) or isinstance(crs, basestring):
        try:
            out = pyproj.Proj(crs)
        except RuntimeError:
            try:
                out = pyproj.Proj(init=crs)
            except RuntimeError:
                out = None
    else:
        out = None
    return out