[xmqdtrba] Analyzing complexity

We imagine a complicated object which changes state over time.

A projection omits or compresses some of the details of the state.  Some state components are combined with a function which is probably lossy, perhaps the constant function which is equivalent to omitting those components entirely.  Famously, projecting a higher dimensional object to a lower dimension.

Invariants remain true regardless of the state changes.  An invariant could be imagined as a (boring) projection whose appearance never changes.

These techniques could be applied to describe anything complex, not just geometric.  Any other tools?