Suppose I have an equational derivation of $t = u$. There are two ways to prove this.
I can show it using a 'sequence of equations' \begin{align*} t_1 &= u_1\\ t_2 &= u_2\\ t &= u \end{align*}
But I can also show it by $$ t = \ldots = \ldots = u $$ What would be a proper way to call such a derivation?