Changes from July 26 meeting

[daira]

• Use $\rightarrow$ instead of $\mapsto$ to indicate function types.
• Consistent use of $\mathrel{⦂}$.
• In the definition of a multivariate polynomial, $c_z$ should not be zero.
• Define $m'_f$ and require fixed concrete columns to be on the left.
• Add a forward reference from the table describing instances to the section that defines multivariate polynomials.
• Spelling exceptions for the LTeX vscode extension.
• Add hints as an explicit argument to ok_for.