A manifest variable reference is itself defined as a variable reference with
a single, unambiguous definition of its value,
which is itself a manifest expression.
The single, unambiguous definition is particularly relevant in procedural languages, where pointer analysis and/or data flow analysis is required to find the expression that defines the variable value. If several defining expressions are possible (e.g. because the variable is assigned in a condition), the variable reference is not manifest.
See also
Polytope model which requires manifest loops and conditions