Bibcode:2000NIMPB.171...60S. doi:10.1016/s0168-583x(00)00005-7. Usukura, J.; K. Varga; Y. Suzuki. Signature of the existence of the positronium molecule. Physical
PMID 21349853. doi:10.1074/jbc.M110.206813 . Zerrad L, Merli A, Schröder GF, Varga A, Gráczer É, Pernot P, Round A, Vas M, Bowler MW (April 2011). "A spring-loaded