For example the defintion of a conjugate transpose/Hermitian transpose of a matrix. I can either take it's conjugate and then transpose it or the other way.
${\displaystyle {\boldsymbol {A}}^{\dagger }}={\displaystyle {\boldsymbol {A}}^{\mathrm {H} }=\left({\overline {\boldsymbol {A}}}\right)^{\mathsf {T}}={\overline {{\boldsymbol {A}}^{\mathsf {T}}}}}$
Let $f(B):=B^H, g(B):=\overline{B}$ and $h(B):= B^T.$
Then
$$f(A)=h(g(A))=g(h(A)).$$
Hence
$$f=h \circ g = g \circ h.$$