[m-messer]

Ports the parsing half of compareExpressions#276 (inequalities and !=) and #278 (chained equalities) to expression_parsing. There is one commit for each. The grading, feedback tags and preview stay in compareExpressions.

expression_parsing (#276)

• parse_expression reads <, <=, >, >= and != as the unevaluated SymPy relations.
• Two inequalities that point the same way (1 < x <= 5) give And of both.
• ≠, ≤ and ≥ are normalised to !=, <= and >=.
• Before, x != 5 was read as Eq(factorial(x), 5), and x <= 5 failed to parse.
• split_relations(expr, error) (exported, along with RELATIONAL_OPERATORS) splits out the operands and checks the rules. It rejects a chain that points both ways, more than two inequalities, =/!= combined with another relation, and an empty operand.

expression_parsing (#278)

• x = y = z gives And(Eq(x, y), Eq(y, z)) from both parse_expression and parse_latex. Before, more than one = raised an error.
• A single = still gives a bare Equality.
• An empty side (x = = y) is an error, and so is a chain that mixes = with another relation (x = y < z).
• The parity check's a=b=c expected change is updated to record the chain.

Downstream (compareExpressions)

• Without the #276/#278 grading ported, an inequality or a chain reaches check_equality, which handles only Equality. The app ports stack on #289 after the pin bump to rc4.

Verification

• ruff, format and mypy are clean. All package tests pass, and so does the parity check (0 unexpected, 0 mismatched).

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