- Systematic use of duality
algebra/spectrum, vector space/dual vector space, bigebra/dual bigebra
- Quantization methods
real configuration spaces/complex phase spaces
- Size of an object described by middle character
E = finite dimension, A = Banach structure, I = Hilbert structure
- Various overline/underline accents for complementary notions
norm/unit vector, trace/traceless part, interior/boundary

More details can be found in the The Notation and Filing System.