Lean-Workbook Syntax 79360: The finite sum of powers of two

For every natural $n$, $\sum_{i=0}^{n-1}2^i=2^n-1$.

Source: Lean-Workbook row lean_workbook_plus_79360 (Apache-2.0), original record. This corrected declaration replaces the obsolete finite sum/product binder in with ∈ and restores required imports or namespaces. Ranges, casts, quantifiers, and mathematical expressions are preserved.