喂食
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\usepackage[helvratio=.9]{newtxtext}
\usepackage[slantedGreek,subscriptcorrection]{newtxmath}
\usepackage{mathtools}
\mathtoolsset{mathic=true}
\begin{document}
Begin.\\[101.9ex]%%% with 101.8ex, the f-block is on p.1. With 101.9ex, the f-block is on p.2
Consider the following functions:
\begin{align*}
f\colon \mathbb{N}&\to \mathbb{N}\\% allow for a page break after