[[!redirects Sandbox > history]] [[!redirects Sandbox]] < [[nlab:Sandbox]] \tableofcontents \section{Quadratic closures} A field is **quadratically closed** if every non-degenerate monic quadratic function is the product of two monic affine functions. Quadratic closure: Every non-degenerate monic quadratic function is the product of two monic affine functions. \section{Test} Literal basic stuff about high school algebra: * What is a variable? * What are free and bound variables? * What is substitution of terms for variables? \section{Variables} A variable is a symbol $x$ which represents an arbitrary instantiation of a type $T$. Variables are thus types and written as $x:T$. Variables are usually found in the context, as $\Gamma, x:T, \Delta \vdash \mathcal{J}$ for arbitrary judgment $\mathcal{J}$. \section{Free and bound variables} \section{Substitution} \section{Change of bound variables} category: redirected to nlab