Change the wording to closer correspond to C++ types and concepts

Author: NlightNFotis

doc/architectural/central-data-structures.md

@@ -9,11 +9,19 @@ CBMC and the assorted CProver tools.
 The `goto_modelt` is the main data structure that CBMC (and the other tools) use to
 represent GOTO-IR (the `GOTO` Intermediate Representation).
 
-A `goto_modelt` is effectively a product type, consisting of:
+A `goto_modelt` is effectively a pair, consisting of:
 
-* A list of GOTO functions (pseudocode: `type goto_functionst = list<goto_functiont>`)
-* A symbol table containing symbol references for the symbols contained in the
-  GOTO functions (pseudocode: `type symbol_tablet = map<identifier, symbolt>`).
+* A list of GOTO functions,
+* A symbol table containing symbol references for the symbols contained in the GOTO functions.
+
+In pseudocode, the type looks this:
+
+```js
+type goto_modelt {
+  type goto_functionst = list<goto_functiont>
+  type symbol_tablet = map<identifier, symbolt>
+}
+```
 
 The abstract interface of `goto_modelt` is outlined in the file
 [`src/goto-programs/abstract_goto_model.h`](../../src/goto-programs/abstract_goto_model.h).