Fig. A.1
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Four Planck functions (times x) as a functionof the dimensionless frequency parameter x. The Planck function has the 0 index, and the three indices label the three consecutive Planck function derivatives. Hence, we have plotted x f(x), x g(x), x g(x) (h(x) − 1), and 
, where the functions f, g, and h are defined in Eqs. 5, 7, and 10.
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