Answer
The program contains an undeclared variable.
Work Step by Step
1. There is not a missing semicolon and there is not a misspelled variable name. (by (c) and (d) and definition of ∧ )
2. It is not the case that there is a missing semicolon or a misspelled variable name. (by (1) and De Morgan’s laws)
3. There is not a syntax error in the first five lines. (by (b) and (2) and modus tollens)
4. There is an undeclared variable. (by (a) and (3) and elimination)
