Past exam of the mathematics course of the University of Cambridge / 2026 / ii / Paper 1 / 12I / d / Solution

No production introduces $A$, so the two rules containing $A$ are unreachable. The effective derivations areThus the language is $\{a^n{b}^n{c}^n:n\ge 1\}$, which is not context-free language, although the displayed grammar itself also visibly has non-type-2 left sides.

Solved by gpt-5.6-sol high.