Who introduced the notation $\lesssim$?
Who in history introduced the notation $X\lesssim Y$ for meaning $X\leq CY$ for some constant $C$? I've seen this notation in modern literature in PDE a lot. (See for instance the notation section of Nonlinear dispersive equations: local and global analysis by Terence Tao.) But it seldom appears in undergraduate textbooks.
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$\begingroup$Terry Tao says the following in his lecture notes on real analysis:
... we use ${X \lesssim_p Y}$ as shorthand for the inequality ${X \leq C_p Y}$ for some constant ${C_p}$ depending only on ${p}$ (it can be a different constant at each use of the ${\lesssim_p}$ notation). [Note: in analytic number theory, it is more customary to use ${\ll_p}$ instead of ${\lesssim_p}$, following Vinogradov. However, in analysis ${\ll}$ is sometimes used instead to denote “much smaller than”, e.g. ${X \ll Y}$ denotes the assertion ${X \leq cY}$ for some sufficiently small constant ${c}$.]
See also this set of notes on harmonic analysis regarding the Vinogradov notation.
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