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## Main Question or Discussion Point

if D means the derivative respect to x , is always licit to use this operator ??

for example Ramanujan obtained his Master theorem from the integral equality

[tex] \int_{0}^{\infty} dx e^{-ax} x^{m-1} = \Gamma (m) a^{-m] [/tex]

by just replacing the 'a' number by the operator exp(D) and expanding exp(-exp(x) but is this valid ?? , can we always replace real numbers by operators ??

for example Ramanujan obtained his Master theorem from the integral equality

[tex] \int_{0}^{\infty} dx e^{-ax} x^{m-1} = \Gamma (m) a^{-m] [/tex]

by just replacing the 'a' number by the operator exp(D) and expanding exp(-exp(x) but is this valid ?? , can we always replace real numbers by operators ??