A prefix expression tree showing an expression can be supplemented to also display the expression in infix notation. A variable capacitive device having a fixed vertically-inclined silicon-bearing compound electrode and a movable vertically-inclined silicon-bearing compound electrode produced by arranging a sacrificial layer on a base silicon-bearing compound electrode, depositing a grown silicon-bearing compound electrode on the sacrificial layer, and etching the sacrificial layer. The cages each include a ring and a plurality of axial projections having axial free ends.