1965 - James Gunn[?] and Bruce Peterson[?] use observations of the relatively low absorption of the blue component of the Lyman-alpha line[?] from 3C9[?] to strongly constrain the density and ionization state of the intergalactic medium
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The symbol
<math>\pm \sqrt {b^2-4ac}</math>
in the formula should be understood as "either of those element(s) of the field whose square equals b2 - ...