10 2. ALGEBRAIC DISCRETE MORSE THEORY

Before we proceed to the applications, we give a simple example that shows

that the finiteness assumption of Theorem 2.4 indeed is needed.

Example 2.5. Let C• be the (non-reduced) chain complex of the simplicial

complex triangulating the real line by 1-simplices [i, i+1] for i ∈ Z. Then C0 and C1

are free Z-modules of countably infinite dimension. It is easily seen that matching

each 0-cell {i} with the 1-cell [i, i+1] yields an acyclic matching. The corresponding

Morse complex is constant 0. In particular, its homology in dimension 0 is 0 being

different from the 0-th (non-reduced) homology group of the real line, which is Z.

In the following chapters we will use the conclusions of Theorem 2.2 and 2.4

in order to construct minimal free resolutions without explicitly referring to the

theorems.