English: Given a monad ${\displaystyle (T,\eta ,\mu )=(T:{\mathcal {C}}\rightarrow {\mathcal {C}},\ \eta :{\mbox{id}}_{\mathcal {C}}\rightarrow T,\ \mu :T^{2}\rightarrow T)}$, consider a Kleisli category ${\displaystyle {\mathcal {K}}}$ over that monad. Morphisms ${\displaystyle {\tilde {f}}:A\rightarrow B}$, ${\displaystyle {\tilde {g}}:B\rightarrow C}$, and ${\displaystyle {\tilde {h}}={\tilde {g}}\circ {\tilde {f}}:A\rightarrow C}$ in ${\displaystyle {\mathcal {K}}}$ correspond to morphisms ${\displaystyle f:A\rightarrow TB}$, ${\displaystyle g:B\rightarrow TC}$, and ${\displaystyle h:A\rightarrow TC}$ in ${\displaystyle {\mathcal {C}}}$, respectively. The composition rule is ${\displaystyle {\tilde {g}}\circ {\tilde {f}}={\widetilde {(\mu _{{\text{cod}}(g)}\circ Tg\circ f)}}}$.