Definition. \(T\)-monoid [mde-NO9S]

A \(T\)-monoid in a virtual double category, for a monad \((T, \eta , \mu )\) on a virtual double category, is a monoid in the loose (horizontal) Kleisli virtual double category of \(T\).

It comprises in other words,

  • An object \(X_0\),
  • a loose morphism \(X : X_0 \nrightarrow TX_0\),
  • a unit cell,
  • a multiplication cell,
  • satisfying unitality and associativity equations.