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I am using \documentclass{report} and \usepackage{amsmath}. My problem is relation symbols such as \backsim \lesssim \gnsim are not working. Everytime I try to use such symbols error comes !Undefined control sequence. Please guide.

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up vote 9 down vote accepted

I'll just turn this into an answer.

amsmath provides very few symbols, so in most cases [1] you need to load both amsmath and amssymb

[1] Some font packages provide the exact same set of symbols as amssymb, in which case you need to either not load amssymb at all, or make sure amssymb is loaded first, such that the font package and override the symbols with the ones suitable for this particular font. (the kpfonts package is an example of this).

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