Theory was developed by Turkish quantum chemist Oktay Sinanoğlu in the early 1980s and first published in 1983.
The theory was like a new language of quantum mechanics by the exact definition of Hilbert space.
This VIF theory also connected both delocalized and localized molecular orbital schemes into a unified form in an elegant way.
Chemical deductions are made from a VIF picture with the application of two pictorial rules.
Transformation by the two rules preserves invariants crucial to the characterization of the molecular electronic properties, the numbers of bonding, non-bonding, and anti-bonding orbitals and/or the numbers of doubly, singly, and unoccupied valence orbitals.