@article{IUPAC+S05434+2019,
url = {https://doi.org/10.1351/goldbook.S05434},
institution = {International Union of Pure and Applied Chemistry (IUPAC)},
year = {2019},
title = {σ, π (sigma, pi)},
doi = {doi:10.1351/goldbook.S05434},
edition = {3.0.1}
}