Update src/appendix/glossary.md

Co-authored-by: Who? Me?! <mark-i-m@users.noreply.github.com>

src/appendix/glossary.md

@@ -63,7 +63,7 @@ rib <div id="rib"/>                      |  A data structure in the name resolve
 sess <div id="sess"/>                    |  The compiler session, which stores global data used throughout compilation
 side tables <div id="side-tables"/>      |  Because the AST and HIR are immutable once created, we often carry extra information about them in the form of hashtables, indexed by the id of a particular node.
 sigil <div id="sigil"/>                  |  Like a keyword but composed entirely of non-alphanumeric tokens. For example, `&` is a sigil for references.
-soundness <div id="soundness"/>          |  A technical term in type theory. Roughly, if a type system is sound and a program type-checks, it is type-safe. That is, one can never (in safe rust) force a value into a variable of the wrong type. (see "completeness").
+soundness <div id="soundness"/>          |  A technical term in type theory. Roughly, if a type system is sound, then a program that type-checks is type-safe. That is, one can never (in safe rust) force a value into a variable of the wrong type. (see "completeness").
 span <div id="span"/>                    |  A location in the user's source code, used for error reporting primarily. These are like a file-name/line-number/column tuple on steroids: they carry a start/end point, and also track macro expansions and compiler desugaring. All while being packed into a few bytes (really, it's an index into a table). See the Span datatype for more.
 substs <div id="substs"/>                |  The substitutions for a given generic type or item (e.g. the `i32`, `u32` in `HashMap<i32, u32>`).
 tcx <div id="tcx"/>                      |  The "typing context", main data structure of the compiler. ([see more](../ty.html))