@article{SF_1982__24_134547,
     author = {P.R. Jones},
     title = {A graphical representation for the free product of {E-unitary} inverse semigroups.},
     journal = {Semigroup forum},
     pages = {195--222},
     publisher = {mathdoc},
     volume = {24},
     year = {1982},
     zbl = {0486.20035},
     url = {http://geodesic.mathdoc.fr/item/SF_1982__24_134547/}
}