@article{10_4064_ap_21_3_309_324,
     author = {J. {\L}awrynowicz},
     title = {On a class of quasi-conformal mappings with invariant boundary points, {I.} {The} class $E_Q$ and and the general extremal problem},
     journal = {Annales Polonici Mathematici},
     pages = {309--324},
     publisher = {mathdoc},
     volume = {21},
     number = {3},
     year = {1968},
     doi = {10.4064/ap-21-3-309-324},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/ap-21-3-309-324/}
}