Lean-Workbook Syntax 66744: Positivity of finite products

If a natural-number sequence $b_i$ is positive at every index, then $\prod_{i=0}^{j-1}b_i>0$ for every natural $j$, with the empty product equal to 1.

Source: Lean-Workbook row lean_workbook_plus_66744 (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.