  We discuss various concepts of $\infty$-homotopies, as well as the relations
between them (focussing on the Leibniz type). In particular
$\infty$-$n$-homotopies appear as the $n$-simplices of the nerve of a complete
Lie ${\infty}$-algebra. In the nilpotent case, this nerve is known to be a Kan
complex \cite{Get09}. We argue that there is a quasi-category of
$\infty$-algebras and show that for truncated $\infty$-algebras, i.e.
categorified algebras, this $\infty$-categorical structure projects to a strict
2-categorical one. The paper contains a shortcut to $(\infty,1)$-categories, as
well as a review of Getzler's proof of the Kan property. We make the latter
concrete by applying it to the 2-term $\infty$-algebra case, thus recovering
the concept of homotopy of \cite{BC04}, as well as the corresponding
composition rule \cite{SS07}. We also answer a question of \cite{BS07} about
composition of $\infty$-homotopies of $\infty$-algebras.
