\begin{definition}[Definition:Harmonic Sequence]
A '''harmonic sequence''' is a sequence $\sequence {a_k}$ in $\R$ defined as:
:$h_k = \dfrac 1 {a + k d}$
where:
:$k \in \set {0, 1, 2, \ldots}$
:$-\dfrac a d \notin \set {0, 1, 2, \ldots}$
Thus its general form is:
:$\dfrac 1 a, \dfrac 1 {a + d}, \dfrac 1 {a + 2 d}, \dfrac 1 {a + 3 d}, \ldots$
\end{definition}