[1] Douglas J., Jr.: 
On the numerical integration of $u_{xx} + u_{yy} = u_t$ by implicit methods. J. Soc. Indust. Appl. Math. 3(1955), 42-65. 
MR 0071875[3] Douglas J., Jr., Dupont T.: 
Alternating-direction Galerkin methods on rectangles. Numerical Solution of Partial Differential Equations II (Burt Hubbard, ed.), Academic Press, New York, 1971, pp. 133-214. 
MR 0273830 | 
Zbl 0239.65088[5] Douglas J., Jr., Peaceman D. W.: Numerical solution of two dimensional heat flow problems. A.I.Ch.E. Jour 1 (1955), 505-512.
[7] Douglas J., Jr., Santos J. E., Sheen D., Bennethum L. S.: 
Frequency domain treatment of one-dimensional scalar waves. Mathematical Models and Methods in Applied Sciencis (1993), to appear. 
MR 1212938 | 
Zbl 0783.65070[8] Peaceman D. W.: 
The numerical solution of parabolic elliptic differential equations. J. Soc. Ind. Appl. Math. 3 (1955), 28-41. 
DOI 10.1137/0103003 | 
MR 0071874