Question: Whats with these symbols?

In the Maple 11 user manual, at the beginning, on page 1 is an integral of sin(1/x)dx from zero to pi. The solution is given as an expression including -Ci(1/Pi). No definition or explanation is given for Ci. So my obvious question is what in the world is this Ci? I suspect it is a constant but if that is true, why doesn't the program present it's value? Then on page 20 is another integral where the answer is given as 1/2 erf(1)sqrt(pi). Here again, there is no explanation of what in the world erf(1) means, so what in the world is erf(1)?
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