# §6.1 Special Notation

(For other notation see Notation for the Special Functions.)

$x$ real variable. complex variable. nonnegative integer. arbitrary small positive constant. Euler’s constant (§5.2(ii)).

Unless otherwise noted, primes indicate derivatives with respect to the argument.

The main functions treated in this chapter are the exponential integrals $\mathop{\mathrm{Ei}\/}\nolimits\!\left(x\right)$, $\mathop{E_{1}\/}\nolimits\!\left(z\right)$, and $\mathop{\mathrm{Ein}\/}\nolimits\!\left(z\right)$; the logarithmic integral $\mathop{\mathrm{li}\/}\nolimits\!\left(x\right)$; the sine integrals $\mathop{\mathrm{Si}\/}\nolimits\!\left(z\right)$ and $\mathop{\mathrm{si}\/}\nolimits\!\left(z\right)$; the cosine integrals $\mathop{\mathrm{Ci}\/}\nolimits\!\left(z\right)$ and $\mathop{\mathrm{Cin}\/}\nolimits\!\left(z\right)$.