Basic Category Theory
《Basic Category Theory》 · 第 41 页 · Definition 2.1.1
An adjunction between \(\mathcal A\) and \(\mathcal B\) consists of functors \(F:\mathcal A\to\mathcal B\) and \(G:\mathcal B\to\mathcal A\), together with a bijection \(\mathcal B(F(A),B)\cong\mathcal A(A,G(B))\) natural in \(A\) and \(B\).