I got it to work with

\mathop{\underline{\lim}}_{n \to \infty} f_n(x)

Above looks exactly how I want it to look, but initiating operators twice is odd and it's far from simple

\lim_{n \to \infty} f_n(x)

Or is it alright?


If you are using the amsmath package, you don't have to define a new operator; the package offers \varliminf with the correct spacing:


\[ \varliminf_{n \to \infty} f_n(x) \]

enter image description here


If this is used often, then declare it as a math operator. It promotes consistency (see Consistent typography) and ease-of-use:

enter image description here

\usepackage{amsmath}% http://ctan.org/pkg/amsmath
\[ \mathop{\underline{\lim}}_{n \to \infty} f_n(x) \]
\[ \inflim_{n \to \infty} f_n(x) \]

See the amsmath documentation (section 5.1 Dening new operator names, p 17) for the use of/difference in DeclareMathOperator and its starred variant.

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